If tiki was working fine in 6.0, I don't understand why it shouldn't do it in 6.1. Can you double check that you don't miss any file uploaded to your site?
If you have a backup of all your files (or the 6.0 you installed initially), can you try re-installing that 6.0, to see if the problem is solved?
If so, then, upload the different files (with some good ftp program, telling it to make a synchronization of files from your local 6.1 towards the 6.0 on the server).
Alternatively, you could try to use adodb instead of pdo in the db connection (but if it was working for you in 6.0, that shouldn't be an issue).
See this faq to see if it helps:
Reply back if you make any progress, please.