Edit your

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSDTC\MTxOCI keys to contain the following:

a) "OracleOciLib"="oci.dll"

b) "OracleXaLib"="oraclient9.dll".

c) "OracleSqlLib"="orasql9.dll"

Then reboot your server. (I'm assuming the Oracle linked server is Oracle 9i)

Victor