User are unable to logon and get Event ID 7 and 8 in the event logs, with errors "The template named: UsernamePassword could not be found." and an exception "The creation of a form failed".

Check if the IIS_IUSRS group has "List folder/read data" permission on the "C:\Windows\Temp" folder and free up disk space on StoreFront server.

Problem Cause

During StoreFront startup, it tries to load form templates after compiling them into assemblies and saving to "C:\Windows\temp" directory so issue reading/writing to/from the folder will cause these symptoms. This can is usually caused by a permissions issue, however in this case the server was running out of disk space which is what caused the issue/prevented write access to the temp folder.