Connection problems after upgrade to 3.10

I’'ve had a failed update from 3.01 to 3.10 today. The upgrade looked succesful, ldap authentication against a W2K domain worked (something which I expected to break). I have around 50 concurrent users. Around 5 of these were not able to get reliable connections to the server. Their clients were looping online / offline continually with a few seconds between each.

In all cases the client was soapbox 2.5. I rolled the server back to 3.01 and these users can now connect again. Has anyone come accross anything like this?