Error uploading to Xamarin Test Cloud

Hi,

I'm trying to get started with Xamarin Test Cloud and my iOS app.
I've followed the iOS Quickstart guide and succesfully created a test locally using the iOS simulator.
So far, everything is working beautifully.

However, when trying to upload the test to the test cloud, Xamarin Studio reports Error uploading MyAppName-MyAppVersion.ipa... in the "Test Cloud" panel/console. It then continues to try a second time and fails again. After the second try, there's a bit more information available in the "Test Cloud" panel:

Negotiating file upload to Xamarin Test Cloud.
Posting to https://testcloud.xamarin.com/ci/anonymous_uploads

Uploading Xamarin.UITest.dll ... Already uploaded.
Uploading nunit.framework.dll ... Already uploaded.

Error uploading MyAppName-MyAppVersion.ipa...

Error uploading MyAppName-MyAppVersion.ipa...

Uploading MyAppName.UITests.dll... 100%
Uploading MyAppName.UITests.dll... 100%

Uploading MyAppName... 10%
Uploading MyAppName... 20%
Uploading MyAppName... 30%
Uploading MyAppName... 40%
Uploading MyAppName... 50%
Uploading MyAppName... 60%
Uploading MyAppName... 70%
Uploading MyAppName... 80%
Unexpected character encountered while parsing value: <. Path '', line 0, position 0.
Uploading MyAppName... 90%
Uploading MyAppName... 100%
Uploading MyAppName... 100%

The .ipa exists in the expected directory and it's size is around 86MB.
I'm on a wired internet connection so I think we can rule out connectivity issues.

Any idea what's going on here?

thx,
felix