When making a request to:
https://outlook.office365.com/EWS/OData/Users(';<user>@<domain>.onmicrosoft.com')/Contacts

If the user has a Room as a contact. i.e. From https://outlook.office365.com, go to People/Directory/All Rooms. Select a room, then "Add to Contacts"

Then the request fails with:

code=500
data=
{ "error" : { "code" : "ErrorInternalServerError",
"innererror" : { "message" : "Object reference not set to an instance of an object.",
"stacktrace" : " at Microsoft.Exchange.Services.OData.Model.ContactSchema.<.cctor>b__2c(Entity e, PropertyDefinition ep, ServiceObject s, PropertyInformation sp)\r\n at Microsoft.Exchange.Services.OData.Model.SimpleEwsPropertyProvider.GetProperty(Entity entity, PropertyDefinition property, ServiceObject ewsObject)\r\n at Microsoft.Exchange.Services.OData.Model.ContactProvider.ItemTypeToEntity(ItemType itemType, IList`1 properties)\r\n at Microsoft.Exchange.Services.OData.Model.ContactProvider.Find(String parentFolderId, ContactQueryAdapter queryAdapter)\r\n at Microsoft.Exchange.Services.OData.Model.FindContactsCommand.InternalExecute()\r\n at Microsoft.Exchange.Services.OData.ODataCommand`2.Execute()\r\n at Microsoft.Exchange.Services.OData.ODataTask.Execute(TimeSpan queueAndDelayTime, TimeSpan totalTime)",
"type" : "System.NullReferenceException"
},
"message" : "Object reference not set to an instance of an object."
} }

After Deleting that contact, then the REST call succeeds

I am prototyping a task pane app for Apps for Office. I intend to deploy this on the desktop version of Excel as well as Excel Online in various browsers (IE, chrome, firefox). Currently, I am unsure of the proper way to test the interaction of my task pane App with the Excel spreadsheet. For instance, when my app inserts a table into the Excel Spreadsheet, what tool should I use to verify that a table was inserted into the sheet. For the desktop version of Excel, Coded UI seems usable. However, for online versions of Excel, it is does not seem possible to resolve cells/objects from the spreadsheet in the browser. It would be great if the Apps for Office team could give guidance, sample projects, or even provide a framework for developers to test their Apps against the various Excel endpoints. Perhaps you could even describe how you test internally. I think providing this sort of information would ultimately raise the quality of the Apps that developers build for the Office store. Thanks!

Developing my first App for Office (specifically Excel) was an experience I found to be unnecessarily difficult. The Trusted App Catalogs user interface in Excel:

File -> Options -> Trust Center -> Trust Center Settings... -> Trusted App Catalogs

Is a giant mess. There's no browse button - just a field to punch in a string that has to be formatted a specific way and only allows network shares and SharePoint remote servers. First off, I was expecting to see a checkbox to "Allow manifest files from untrusted locations" that would then open up a way to select a XML file via the standard Windows "File Open..." dialog within Apps for Office itself. The File Open... dialog handles all sorts of scenarios that are useful and flexible (e.g. it can download remote files via a URL). Excel shouldn't care where the XML file comes from after such a checkbox is checked. Then, if you really truly wanted to define an entire catalog, have a XML index file option where the XML file points at a bunch of other XML files. And while you are at it, add a button that allows a user to export their catalog to an index XML file in the appropriate format (i.e. allow a developer or other qualified IT employee at a company to construct the catalog and then export it). This allows you to get rid of the entire Trusted App Catalogs dialog altogether and have a sane Apps for Office dialog that actually makes sense. The way it is built now also basically stops local computer development of new apps (WTF?) unless the developer knows Windows intimately and can figure out the '\\.\C:\path\to\manifest\' hack that makes a local drive *LOOK* like a network share to the clearly poorly written code behind that dialog. When there are grammatically incorrect strings being emitted, you know the code is crap. Again, the dialog should not exist at all.

Having to restart Excel after making each change to the Trusted App Catalog dialog should have been the first indicator that perhaps the Office Platform team was going about Apps for Office all wrong.

I'm certain that if Bill Gates still worked at Microsoft and sat in on the meeting regarding this non-feature of the Office suite, the F-word counter would surpass whatever the existing record is. This is alpha-quality (at best). Go back and redo.

We keep getting reports and complaints from users that buy our apps but seem to be locked in trial mode. Receiving 1/2 reports a day. We checked that we are receiving trial tokens in the app, but users confirm that they bought the apps. Some are able to reset somehow, but most can't.

This error is also described here (see first review by Rod):
http://office.microsoft.com/en-gb/store/mini-calendar-and-date-picker-WA102957665.aspx

Other recent feedback from user:

"I tried all the usual suspects. Reloaded excel. Refreshed apps in excel. Attempted to repurchase through excel to see if it would kick in. Restarted the computer."

"If my memory is correct, I believe the yellow trial warning box that drops from the top of the screen that prompts you to purchase (which I believe is queued when you try to load data instead of just watching the demo) eventually caught on itself and the 'buy' button turned into a 'refresh' button (or something very similar to that) and where it said '...you are on a trial, click to buy...' it changed to 'you may have purchased this, click to refresh'. As soon as I did that it worked, I think the problem is that the 'you may have purchased this, click to refresh' button isn't appearing on command as I had to try the things I mentioned to get it to kick through (and who knows if what I did did anything, or if it eventually fixed itself). Hope that is clear."

Already opened an issue with office apps support team, but now new information yet.

Can only imagine annoying and demotivating this should be to Office users.

Rui