the video sync signal on video tape is often difficult for scalers, line doublers, and fixed panel devices like LCD/DLP projectors and plasma's to process.

sometimes I will put a TBC (time base corrector) which strips the tape's sync off and reinserts a standard NTSC sync. this would go between the vcr and the receiver.

in some cases, by runnind the VCR seperately to the plasma w/ composite or Y/C will fix this problem.

some VCRs, such as high end JVC models have a TBC built into the unit.

included just for statistical referrence...
I personally have had problems with Sharp VC-S101 and JVC HRS series VCRs to DVDO based line doublers, Fujitsu plasmas, and Pioneer plasmas. Using a Faroudja processor or Faroudja circuit equiped device (such as Marantz VP12S1 projector) has always solved this problem.