I hope your primer dimer problem was solved.
I have some tips for other users including:
Decrease your primer concentration
Re-design primers. Check primers carefully for homo-dimer and hetero-dimer formation with OligoAnalyzer or similar primer software.
Try adding formamide to PCR to denature primers better.
Increase your DNA template concentration.
Increase your PCR annealing temperature.
PCR may benefit by adding DMSO (2-5%).
Also, HotStart PCR has less primer dimers than regular Taq polymerase PCR.
I got this information from PCR Troubleshooting