Excel crash

Hi All,

I need to fix a macro with my company that stopped to work from one day to the other. Excel simply quits without any errormessage, although there is an error handling it.
I added several line to the code that writes out to a text file to see where is the last stage it still works, and I saw, that it writes out even afte the last line of the module. What is more interesing, if works perfectry when I run it step by step with F8.
Once it produced Automation error, but I canot reproduce it. References are ok, nothing special is linked, as the macro is quite simpe: open files and copy paste from them.
Is there any way to find out, what is happening?

thx