There are some duplicated tags due to database corruption and I can't merge

[neil (Neil Lalonde)]

Sounds the same as this topic:

'Tag is Invalid' - likely due to an unspecified plugin

It works fine with one tag, but with more sometimes it won’t allow users to post and gives that error message. You can edit the post afterwards with as many tags as you want, and sometimes it just lets you post. Is there a setting in the backend that i need to change? Maybe the sporadic nature means users can’t create more than one tag at a time, or create a new tag when existing ones are also present. Anyone else encountered this?

There’s a unique index on the tag name column, so it shouldn’t be possible to have duplicate tags. I’m guessing if you did reindex table tags it would fail.

@pfaffman’s process here is probably what you’ll need to do to remove the duplicate tags and fix the indexes.