I have an old i-mac

Question

I have an old i-mac flat screen, with a Pioneer DVD-RW DVR-108.For the last 6 years it has worked perfectly, no problems, but lately it will not make my home movie DVDs, Ican select all the menu options etc, but when I ask it to burn DVD it goes through the process, perhaps 40 minutes, then ejects and tells me that I have error no. 8.It will however burn cds rom files ie fotosAnybody know what error 8 is.ThanksNapper