Addon disconnected message after producing a report

Hi

I have written some forecasting reports for a SAP 2007a customer which creates an excel spreadsheet

They have alot of data and it takes some time to run, maybe 10 minutes or even longer

The report always finishes but they nearly always get a message that the addon is disconnected and options to ignore, restart etc are displayed

Has anyone any ideas why they are getting this please as I can't recreate it on my pc with their data

I wonder if somehow the ui api is timing out and if I had some sort of progress bar might help

Thanks for any help you can give

Regards Andy