Hi,
Please go to IIS Manager (Switch to Content View) to check the files there:
Expand Sites > Exchange Back End > 15.0.620.29 (my Exchange server is Exchange 2013 CU1). Please check whether there are any file folders under themes and Scripts folder. If there is no folder there, please copy the whole folders "Scripts"
and "Themes" or the entire folder of 15.0.620.29 (cu1) folder from Exchange Installation Path /ClientAccess/ ECP/ CU1 folder in a working machine(the same Exchange version) to the update folder on same location.
Please switch to IIS manager Feature View, go to Exchange Back End > ECP home, open Application Settings in /ecp Home, please check whether the value for BinSearchFolders is changed to an invalid value. If so, please change it to:
C:\Program Files\Microsoft\Exchange Server\V15\bin;C:\Program Files\Microsoft\Exchange Server\V15\bin\CmdletExtensionAgents;C:\Program Files\Microsoft Exchange Server\V15\ClientAccess\Owa\bin.
Then run IISReset /noforce from a prompted command window to restart IIS services.
If all above doesnt work, please collect some error logs for further analysis.
Re