Here is some advice MIT made not to long ago that might be of value to your IT people
" there is a proxy server involved. This may be at the school level or above it. A proxy server is different then a router, it terminates HTTP sessions and then makes its own connection to the ultimate destination. It is a "device in the middle". They are often used to cache webpages so that when a bunch of people (say a class full) attempts to access the same webpage, only one copy is fetched from the ultimate destination and then provided to all of the people making the request. They can significantly improve the performance of web page views.
...App Inventor is not a webpage, but a web based application. It can put a lot of stress on a proxy server. When the proxy server becomes overloaded, you will see errors like you are seeing...