Insignia DVD recorder copy protected

Why am I sometimes able to record a movie off of cable onto DVD, but
sometimes the when copying the same movie , the DVD recorder says
"uncopyable". I recorded "The Incredibles" onto a DVR hard drive, and
copied it later from the DVR onto DVD with no problem...but the next
day I tried to make another copy from the same DVR recording, and it
won't let me.

Whenever I get the "uncopyable" warning, it won't let me record
ANYTHING onto DVD (including the local news) until I turn the DVD
recorder off and on again.

I have a Best Buy "Insignia" brand IS-DVD100121 VDR/DVD Recorder.

emulemul@yahoo.com