NEC 2500A v1.7 - which DL FW do you suggest? Problem with reading!

Which FW (the best and safest/no risk) should I use i.e. which do you
suggest?
Where can I get the firmware?

Why can my NEC not read an DVD which has come with a PC-magazine (with shareware/freeware programs)? I have changed 2 times the DVD in the office but all 3 could not be read from my NEC - he blocked my Explorer so that I must to restart the PC.
In other DVD-recorder from my friends the DVD are working well!?

How I can solve it?

Thanks