i'm trying to access the shares on a server. The credential box appears, and i enter in a correct username and password, and i get access denied.

The silly thing is that i can Remote Desktop to the server (using the same credentials), and i can check the Security event log for the access denied errors:

Event Type: Failure Audit
Event Source:   Security
Event Category: Account Logon 
Event ID:   681
Date:       3/19/2011
Time:       11:54:39 PM
User:       NT AUTHORITY\SYSTEM
Computer:   STALWART
Description:
The logon to account: Administrator
 by: MICROSOFT_AUTHENTICATION_PACKAGE_V1_0
 from workstation: HARPAX
 failed. The error code was: 3221225578

and

Event Type: Failure Audit
Event Source:   Security
Event Category: Logon/Logoff 
Event ID:   529
Date:       3/19/2011
Time:       11:54:39 PM
User:       NT AUTHORITY\SYSTEM
Computer:   STALWART
Description:
Logon Failure:
    Reason:     Unknown user name or bad password
    User Name:  Administrator
    Domain:     stalwart
    Logon Type: 3
    Logon Process:  NtLmSsp 
    Authentication Package: NTLM
    Workstation Name:   HARPAX 

Looking up the error code (3221225578), i get an article on Technet:

Audit Account Logon Events By Randy Franklin Smith

...

Table 1 - Error Codes for Event ID 681

Error Code  Reason for Logon Failure
3221225578  The username is correct, but the password is wrong.

Which would seem to indicate that the username is correct, but the password is wrong.

i've tried the password many times, uppercase, lowercase, on different user accounts, with and without prefixing the username with servername\username.

What gives that i cannot access the server over file sharing, but i can access it over RDP?