There are a number of different issues that can create problems with Active Directory:

When someone has troubles and unclear as to why I usually suggest the following:
Run diagnostics against your Active Directory domain.

If you don’t have the support tools installed, install them from your server install disk.
d:\support\tools\setup.exe

Run dcdiag, netdiag and repadmin in verbose mode.
-> DCDIAG /V /C /D /E /s:yourdcname > c:\dcdiag.log
-> netdiag.exe /v > c:\netdiag.log (On each dc)
-> repadmin.exe /showrepl * /verbose /all /intersite > c:\repl.txt
A quick little dump repadmin /replsum > c:\replsum.txt
-> ADReplStatus
-> dnslint /ad /s “ip address of your dc”

**Note: Using the /E switch in dcdiag will run diagnostics against ALL dc’s
in the forest. If you have significant numbers of DC’s this test could
generate significant detail and take a long time. You also want to take
into account slow links to dc’s will also add to the testing time.

When complete search for fail, error and warning messages.
DCDiag explanation
http://blogs.technet.com/b/askds/archive/2011/03/22/what-does-dcdiag-actually-do.aspx

Description and download for dnslint
http://support.microsoft.com/kb/321045

ADReplStatus Download and Description
http://www.microsoft.com/en-us/download/details.aspx?id=30005
http://windowsitpro.com/active-directory/active-directory-replication-status-tool-ad-utility-weve-all-been-waiting-almost

If you are working with folks in a forum and will be posting log errors consider using Skydrive and then include the link to the logs in the post.

http://explore.live.com/windows-live-skydrive