I wanted to add that there are situations when a machine has an older version of the Oracle client and when you go to install the newer 11g version that no amount of finagling will make that linked server work. This is usually because the registry libraries are still pointed to an old version of oracle client dll files. By doing a little registry surgery to redirect the oracle libraries to the correct updated dll versions installed with the 11g client, the linked server will then start working.

1. Open Regedit32

2. navagate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSDTC\MTxOCI:

3. if OracleXaLib is set to xa80.dll then update itto OraClient11.dll

4. if OracleSqlLib is set to SqlLib80.dll then update it to orasql11.dll

5. Navagate to HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\MSDTC\MTxOCI

6. if OracleXaLib is set to xa80.dll then update itto OraClient11.dll

7. if OracleSqlLib is set to SqlLib80.dll then update it to orasql11.dll

Just one more thing to check when troubleshooting linked server issues.