DVD recorder won't play DVD+R discs

[dubliner]

I recently used some DVD-R discs in my DVD recorder, - I had previously only used +R discs.
Now the DVD Recorder will not play any +R discs, even those recorded since I used the -R discs - it says they are blank. This includes discs that I had previously watched successfully.
Any ideas anyone? Thanks

[Wak]

Have you tried finalising the discs as soon as you finish recording them?
I understand that DVD discs which are not finalised will not play on any other DVD player apart from the one which recorded them.
However, if you record on a +r disc and then record again on a -R disc without finalising the first +R disc then probably the recorder will not recognise the +R once it has be changed over from +R to record on -R, if you see what I mean?
I would suggest that you record something on to a +R DVD and then finalise it, Then put in the other unfinalised +R DVDs and try to finalise them while the recorder is set for +R discs.
Hope this helps.

[dubliner]

Thanks a lot WAK, - the steps you suggested didn't work, but i'm trying out various permutations of your idea - a very helpful suggestion.