We have recently migrated one of our IIS applications with SQL database on background from Windows 2003 to Windows 2008 R2. And it stopped talking to database. Same ports opened, same ODBC connector created, but no data in any fields in web application
The reason was simple as well as the solution: It was 32-bit application, but Windows 2008 R2 uses 64-bit ODBC connectors by default. Microsoft in the KB942976 article says that for the 32-bit ODBC connectors you should use the 32-bit version of ODBC Administrator tool (Odbcad32.exe), located in the %systemdrive%\Windows\SysWoW64 folder.