I installed Sql Server Reporting Services 2008 R2 on the report server, then installed Oracle client 220.127.116.11.
I copied across a valid tnsnames.ora file, and verified connectivity with both sqlplus and tnsping.
However, trying to connect to one of the Oracle databases from within SSRS I got:
System.Data.OracleClient requires Oracle client software version 8.1.7 or greater
…helpfully highlighted in an angry red.
Fix is fairly straightforward – SSRS hadn’t picked up the change to %PATH% done by the Oracle install yet, so the fix was to re-start the SSRS service.
Pic: From an old out-of-copyright book called ‘Memorials of Old Wiltshire’