Microsoft's dial up net
working, part of windows, has a built in set of error codes that allow you to troubleshoot
issues with connectivity. One of the most common codes you run into at a
help desk is error
691, printed below.
691 - Access denied because username and/or password is invalid on the domain.
Seemingly simple this
error is still confusing enough to account for three or four c
alls a day where I work.