Today TOAD kept telling me it couldn’t load oraclient9.dll in the oracle home I was in (I was connecting to a 9i database), and I noticed that the file had a different length than the other two I found on my system. I copied one of those in the oracle home it was looking and it worked.
Unfortunately the lsnrctl also uses that file and expects the old version.
I ended up using a different home for TOAD to use the tnsnames.ora from.