Pro Maps causes ASP error, and the solution
I was trying to use Pro Maps with a recordset. When I tested my page only the background of the page loads, and I had to do a view source to see the error message:
Microsoft VBScript runtime error '800a005e'
Invalid use of Null: 'CStr'
It turns out that empty fields in the database aren't handled gracefully by this extension (in ASP anyway) - so the simple solution is to ensure that all fields referenced by the extension are complete.