I had this happen to me a few times too.  One time it was a spam bots post that it claimed I was following.  I still have copies of the...

Good thoughts with that Thom.  SQL Injection, while unlikely in a NVARCHAR(19), could occur.  Your solution does eliminate the risk involved of SQL injection.
I suppose if you knew that...

I could be wrong, but I think you will need to build this as dynamic SQL.  That is:
DECLARE @query varchar(255)
DECLARE @comp_cod nvarchar(19) = N'2,3'
SELECT @query...

Adding to what Sue_H said, and expanding on what Steve Jones said, I tend to avoid ms_foreachdb (for the reasons that Sue_H posted) and would much rather write my own...

Nested queries can be problematic as well.  Might want to use a CTE or a temp table to store the nested query which may give better results.  Since you are...

To me, it sound then like audrey.abbey is likely correct...

Can you replicate the problem on another computer?
If you can replicate the problem, it makes me think the problem is not related to the end users computer.
If you...

A quick google of that error brought me to this:
https://technet.microsoft.com/en-us/library/ms187005(v=sql.105).aspx
basically - update SSMS, possible network issues, server setting may need changing (depending on the windows server version).

The database they were connected to had auto-close set to false, correct?  I believe that is a database level setting...  I am just thinking if they are running a query...