Asp.Net Deployment IIS 6

[Guest]

I'm trying to deploy an asp.net application to a windows 2003 web server.
We have 2 servers (DEV and UAT) with Windows 2003 installed. I don't have
any problems during deployment on neither of them. When I try to access the
app on DEV it works correctly, but am having problems when accessing from
UAT. This application is using class libraries. The first page comes up
fine, but as soon as i go to the page which tries to use the class library, a
null reference exception gets thrown. It appears that something is preventing
the web app to call the class library. I've gone through all the site and
security settings, comparing DEV and UAT to no avail.
This is what's in the log:

2006-09-12 14:41:46 172.73.222.132 GET
/AppName_setup/Uploads/BatchDetails.aspx 443 - 172.52.12.143
Mozilla/4.0+(compatible;+MSIE+6.0;+Windows+NT+5.1;+SV1;+.NET+CLR+1.0.3705;+.NET+CLR+1.1.4322;+.NET+CLR+2.0.50727;+InfoPath.1) 401 2 2148074254
2006-09-12 14:41:46 172.73.222.132 GET
/AppName_setup/Uploads/BatchDetails.aspx 443 AD\lastnamef 172.52.12.143
Mozilla/4.0+(compatible;+MSIE+6.0;+Windows+NT+5.1;+SV1;+.NET+CLR+1.0.3705;+.NET+CLR+1.1.4322;+.NET+CLR+2.0.50727;+InfoPath.1) 500 0 0

Thanks
-j-