If you try to connect to an Oracle Database using the Test Connection button in the Data Sources (ODBC) Control Panel, and get the error [Microsoft][ODBC Driver Manager] Driver's SQLAllocHandle on SQL_HANDLE_ENV failed, try the following suggestions:

Assume Oracle Client in c:\OraClient folder and web folder as c:\inetpub\wwwroot

1. c:\inetpub\wwwroot must have Read and Execute privlege for IUSR user.
2. c:\OraClient must have Read and Execute privlege for IUSR user.
3. The environment PATH variable must have C:\OraClient\bin included.
4. Don't forget to restart Web Server