Check Out Item - COR4504406E Error: Another user is currently performing an operation on Item

Hello,

during delivery of a file to Dimensions CM 14.5.3 the connection was lost.

Now it is not possible any more to check out or revise or synchronize the item in the database.

"Check Out Item - COR4504406E Error: Another user is currently performing an operation on Item"

The item is not checked out, the previous version can be downloaded.

The error also occurs if someone else tries to check out.

Is there any invisible lock that can be removed or something similar?

The database is set up with projects. 

Edit: When I try to open any previous versions of the item, it is not possible:

"Browse Item - COR7700243E The specified item revision is not in the project"

But maybe this is another problem, independently