I'm stumped.
I was trying to replicate a file (corporate wallpaper) to branch offices via SYSVOL (so that workstations in branch offices don't have to pull the file from HO). However, the replication only worked for some RODCs, but failed on other RODCs.
On one failed RODC, I tried forcing replication by using the command ntfrsutl.exe forcerepl DEST_RODC_NAME /r "Domain System Volume (SYSVOL share)" /p dc01.example.com ... and within minutes, the wallpaper appeared!
What could possibly the problem here? Why won't some RODC perform automatic sync?
Take a look into converting from FRS to DFS-R replication. Along the way you'll probably figure out what's going on and why things are taking so long, and move away from the now deprecated FRS sysvol replication.
Here's the article from Microsoft outlining the process: http://technet.microsoft.com/en-us/library/dd640019(v=ws.10).aspx
In particular you can take note of the health checks at the beginning. This might also be a good time to repadmin and be sure that AD itself is resolving all SRV records properly and replicating as it should.