This issue is usually due to an error in the Server Name setting in the iDataCollect app settings. Here are the steps to fix it: 

1. Go to the settings icon on the iPad.
2. Click the iDataCollect icon on the left sidebar.
3. Make sure the Server Name setting looks like it does in the picture below. Some people have seen an extra slash added to it. If you see an extra slash at the end of the server name, please delete it and log in again.

If these steps don't work, download the iForm app, log in with the same username and password, and put idatacollect.iformbuilder.com in the Server Name box.