Excel Closes by itself

For some reason my excel program closes completely by itself, I have it running as a datalogger. It is pulling data out of a PLC via DDE/OPC link, it's just 5 variables.

The Macro is taking the data off one sheet and moving it to the approiate columns on a 2nd sheet. I put in a error trap module to no avail, no errors are shown.

I thought it might be this computer but started on another with the same result. One is 2003 the other is 2002 w/sp-2.

This is my first time using excel like this, can someone look how I have this setup and tell me if it's the way I've done something causing it to just shutdown.

Any Help would be greatly appreciated.