A CMO environment is not able to login and is returning the below error:
Solution (Short term fix)
Follow the below steps -
A. Login to the clients Web Server environment.
B. Go to Filepath C:\Windows\Microsoft.NET\Framework64
C. Search for .Delete - Right click on the file and click open File Location
D. Take a screenshot and make sure you see the Date Modified Date/Time (for the Incident Report / SLA)
E. Change the .Delete filename to .Delete.OLD
F. Login to the affected client environment to confirm it's resolved
Long Term Fix
If hosted Mitratech to raise query with Microsoft - see Jira ticket (CW-10477) from Engineering confirming this.
If on Premise the client is required to raise the query with Microsoft.
Traced the root cause to IIS not clearing out the old DLL file on client's Production Web Server, once updated the CMO production site was accessible again.