I am a Toad for Oracle developer, but I happened to see this post. This is the same as a bug we had in Toad for Oracle.
See here for cause and workarounds.
That's a long thread so I'll summarize:
- Oracle was updated (or you are connecting to a new version)
- You have one of the following in server-side sqlnet.ora
SQLNET.CRYPTO_CHECKSUM_CLIENT=REQUIRED
SQLNET.CRYPTO_CHECKSUM_SERVER=REQUIRED
SQLNET.ENCRYPTION_SERVER=REQUIRED
- You are connecting without an Oracle client.
Change any of these, and it will work.
I'm sure the TDP folks will have it fixed soon. Note to TDP folks: Update your Devart components. 