Cannot create fodlers/subfolders

Cannot create fodlers/subfolders

Hello,
Completely out of the blue, I cannot create folders or subfolders!
Whatever I do, I get this error message:

Error while adding new folder (You are not allowed to create folder with this name.)

Also, when I tried to ask Zoho, I got an error message and the message was not created.
I really don't see any issue with the account, so, I am confused. Is it a system issue?

Update:
I tried with 2 different browsers, I used Private/Incognito mode, cleared cache/cookies. The problem is there.