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.