Ive use this disc retailer for years and never had any problems with their disks.
http://www.svp.co.uk/index.php
They tell you what disc to use with what machine Ive recently bought Ridisc GO4, GO5 in tubs of 50 and hav`nt lost 1.
Toshiba RD-XS32SB TV recorder
NEC DVD RAM burner computer
Just a quickie for anybody who has a Toshiba XS32 recorder and is experiencing DISC NOT RECOGNIZED message ... SEND IT BACK TO TOSHIBA its got the wrong drive in it, even if its out of warranty argue with them...
Try this site for DVD testing tools
http://www.vrforums.com/showthread.php?t=18723