Sometimes we need to move your server from 32 bit operating system to 64 bit, but you have to make sure that your application support 64 bit. I have HR application that connect to our SQL Server 2005, it was running on 32 bit but i had to move it to 64 bit. I set the application and tried to connect to database, it seemed everything went well. But when i try to start the application it said that odbc is not set and bla bla bla…. I check my ODBC setting again, I believed it was there but the question is why? I asked my uncle abot this and it said that some of visual basic application is rely on 32 bit ODBC. If you’re on 64 bit windows system yu must make sure that you’re setting the right ODBC.
- The 32-bit version of the Odbcad32.exe file is located in the %systemdrive%\Windows\SysWoW64 folder.
- The 64-bit version of the Odbcad32.exe file is located in the %systemdrive%\Windows\System32 folder.
Make sure you load the 32 bit ODBC and set your system DSN there. After setting my ODBC connection, I tried to lunch the application one more time and it works this time 
Thank’s to Allah.
source : http://support.microsoft.com/kb/942976
