HELP! VENT / Pfu amplification

[Obaid Y. Khan]

I am trying to amplify a 580 bp fragment from a plasmid template. I get good 
amplification with Taq but when using similar conditions, Vent and Pfu polymerase 
do not work. There is not even a smear on the gel :-(  Has anyone had similar 
problems? I certainly would appreciate any help in this regard. Have tried several 
different annealing temps, Mg++ conc. and even diff. conc. of DMSO in the mix. 
Thanks,
Obaid Khan