Common InfoPath web browser error with error message that lead you to no where.
An error occurred accessing a data source.
An entry has been added to the Windows event log of the server.
Possible root cause:
1. Indeed one of the data source connection is having a problem.
2. Anonymous option under Authentication Provider for particular web application has been enabled.
1. Check all the connection from InfoPath, you can try to preview the form InfoPath Client and
make sure no error occurs. If there is, fix accordingly.
2. Go to SharePoint Central administration > Application Management > Authentication Providers
Clear the check box of anonymous access.