Error 629 is common and is usually the result of a mismatch in what the RAS server requires and how the Phonebook entry is configured at the client end.
The fact that user can 'surf the web' puts the modem driver and resource conflicts out of question...pointing the finger towards the PB-entry. Some unsuspecting users often fiddle with system functions and later forget about it, creating 'strange problems' for admins as a result. Atleast, I've noted this to be the main cause of many end-user problems.
Now what you can do is to create a new PB-entry. Go with defaults. If it doesn't, try lowering down the modem speed and authentication level. Disable PPP LCP extensions, hardware flow control, and compression one at a time.
Hope this helps.
Mubashir
muhammad.mubashir@sbp.org.pk
Imagination is more important than knowledge. - Newton