You may find when upgrading CRM to 7.3SP2 on a Virtual Machine you will encounter the message

 [ODBC Driver Manager] Data source name not found and no default driver


This normally occurs if you are using the full installer on a virtual machine with a restricted account. 


If you use the 7.3SP2 patch installer rather than the full installer it will work around this issue, logging onto the VM using the Administrator account also will work around this issue.