getting a lot of users reporting random errors - at log in - when using the browser back button - clicking between forms.

What should i be looking for to remedy this?

Most likely more detail will be needed.  What "errors" are they getting? 403, 500, 404?

Yes, the errors would be beneficial. A starting point, however, would be reviewing the software logs -- AdminCP -> Support -> Error Logs 

If nothing is revealed there, it's best to have your host look at server-level logs.