I assume you are referring to the html popup on the tinyMCE editor. This is not something I can replicate and I actually use that option quite a lot myself.
Can you determine which browsers these specific users are trying it with. Might be useful to know if they are all using the same one and if there is a problem with that, Then I can look at the tinyMCE development site to see if there are known issues.

OK I asked them what browser and they were on FF, so they went and tried it on IE and told me they received the same issue.

Would you be able to set me up with an account that has the ability to write posts so that I can see this?

If so then please PM credentials to both myself and to ‘Mr Papa’. Please include in the PM a link to your site, a link to this thread and brief reminder of the problem. And one of us will take a look for you.

I can do this but for some odd reason it seems to have fixed itself. My forum guests now say they are able to edit the html and the submit button is there.

Some sort of caching issue probably. IE has some really weird caching going on sometimes.