Long page execution dies

Hi

I have a page which I usually run once per day which takes ~5min to run - a lot of calculations, CFX tags and some writing to database. Recently it does not always get to the end of the job (writes a file as the last part). The browser I run it in either hangs or gives standard "page cannot be displayed" message. I've overridden IIS to allow enough time and CF is not set for timeouts. I have also run "SeeFusion" which shows a 500 server error yet nothing shows up in CFAdmin logs.

As I dont have much to go on, I dont know how to look for an effective cure

Any suggestions?

Thanks

Tim Mortimer