I picked this tip up from Panasonic UK technical help which helped solve my customer's problem (I work for a retailer). It's so simple but effective I thought I ought to share it.

My customer's problem.

When using the RAM disc as supplied with his DMR-E50 he was getting blocky playback on the later part of his recordings. eg. 2nd to 3rd hour of a 3 hour recording.

Panasonic's solution.

The customer was using the RAM disc out of the caddy. Panasonic suggested that it was probably caused by finger prints near the outer edge of the RAM disc surface. True enough other less technically aware members of the customer's family had not handled the discs with care. Once the customer cleaned the discs with a soft cloth and methylated spirit the discs recorded without a problem.

OK it seems obvious to keep the surface of your discs clean but apparently this is a common complaint/solution according to the Panasonic tech I spoke to. Now I know YOU THE DVDRHELP READER are smart enough to take care of your discs, but if other members of your family are handling the discs make sure they handle with care and keep them clean.

Hope this helps