I agree with jhourcle and shmem. As to what causes an error 49(bad credentials)? I think that the problem lies in the registry. From Microsoft's ADAM FAQs:

"When the computer running ADAM is joined to a workgroup, you must set the registry key HKEY_LOCAL_MACHINE\SYSTEM\Current\ControlSet\Control\Lsa\forceguest to 0. The default is 1."

In other words, if your computer is joined to a workgroup and the registry isn't reset to reflect that then you'll get the errors that you are getting. If you're not part of a workgroup, then it's probably a bad DN or password. See:

ADAM FAQs

For LDAP Error Codes see:

LDAP Binding Error Codes

Update: Here's a complete list of LDAP Binding Error Codes:

From Microsoft

And a clearer chart:

LDAP Error Codes