These are illegal bootleg DVDS from a vendor with a terrible reputation. Sadly, it does not surprise me that you are having troubles as others have posted on cc.net that they've had similar problems.
Charlie Chan in London is in great shape on the legal Fox release. If you can return this set I would do so. The legal version might be a couple more dollars but you get what you pay for (better picture quality/transfers, longer lasting media plus the wonderful bonus features that Rush & Dr. Berlin were so involved in). Also supporting the Fox releases will ensure that the entire series gets released.
I have the Vintage Theatre 14 DVD, 42 movie Chan set myself. Looks like DVD-R's, but my entire set plays with no problems. Sure, the quality varies from movie to movie, but more than a few transfers are exceptional for public domain issues.