InfoPath forms and SharePoint are a deadly combination. Only with long association with these two does one understand how both need to be configured to work in harmony !
Here is an example of an error one gets many times while working with these two and webservices. I got "an error occurred while accessing a data source" while accessing my InfoPath forms on SharePoint 2007 site from any machine on the domain other than my SharePoint server where I had deployed my forms.
My forms were accessing a web service deployed onto the server and I was trying to access my SharePoint site from any other machine on the domain.
How I resolved it
Set the Security and Trust to "Domain" . It was set to "automatically determine security level".
you can do this by going to :
Tools -->Form Options -->Security and Trust
Cheers :)!
