Hi Catalin,

From the sounds of it, it would definitely be worth checking what's been installed on those two PCs in the last few days. It would also be worth disabling all add-ins (including COM add-ins) to see if one of them might be causing the interference.

Well, i finally solved the problem, the code runs now fine on all machines...
But i guess it was an unusual bug of that specific version of excel , because even manually protecting or unprotecting that specific sheet caused excel to stop responding.

That sheet has a table, and ALL other sheet rows and columns outside the table was hidden (2003 type .xls workbook). When trying to unprotect the sheet (manually, or by VBA) , excel stops responding and excel.exe process goes to 100% CPU.
I just set all sheet rows and columns to unhidden, and the problem dissapeared.
I couldn't find an answer why excel crashes on a sheet with all rows and columns outside the table hidden.