I stepped through all the upgrade steps from 4.82 on, followed your instructions to proceed past the "We're sorry, but the system experienced an unrecoverable error. Please try again later." on your recommendation to 5.1 then as I reported got the same error again on the 5.1X release to 5.2 step.
I'm not skipping any steps and re-running any of the scripts gives the already exists mysql errors.
I'm doing this on a test site prior to upgrading my live site with duplicated data from the live site.
I'm most confused by the fact that my version is 4.8c and wasn't sure where to start the upgrade from since only 4.82 is listed close to that version. I'll clean out the test install and start again, any suggestions will be most welcome.