What build are you using? I encounter problems since the last build that was released end Nov/beginning Dec. Picture simply stops, audio continues and after about a second or two picture and audio are in sync again. Nerve wrecking and if I enabled Smart de-interlacing, I get nothing but a green screen when playing DVDs. Thus, I have to disable that.

Is there a way to downgrade to the build before that one?

The latest build 2320a has much better smart de-interlacing, but still not quite smooth.
My graphic card is 8600M GT DDR2 256MB 475/400

In that build I get a completely "green" picture when playing DVDs with de-interlacing enabled. BluRays play, but with the problem I described previously.

However, even the 2227 does have some issues that play stops about 1-2 per hour.

I tried another software to play DVDs and BluRay (I am not naming the products as I am not sure about the forums rules with regard to that) to make sure it is not my hardware. It works without any issues for DVD or BluRay. It is a pain having to buy two software products, but considering that with hardware players you have issues with certain BD-generations as well, it is something I am willing to accept.

I tried all of the programs but got the same issue.
It seems de-interlacing needs to a powerful graphic card.

Well, BluRay is supported by nVidia PureView HD so I never had any issues with that. AFAIK PDVD uses nVidia PureView for BluRay playback and the "bug" only occurs with DVDs. That is why it is so strange that the latest PDVD builds give me troubles with HD playback. I also tried different nVidia driver versions, no change.

My card has on-board de-interlacing which makes your statement correct as hardware de-interlacing is definitely better, but requires a card that supports it.