Nero CD-DVD Test Results: What Does It All Mean?

I am a n00b at this stuff, so please bear with my ignorance.
Recently, I have had some burns that were somewhat problematic. Various errors, and what not. Last night, for example, we were watching a copy of The Departed, (terrific flick, by the way). All went well until, with about 15 minutes or so left in the movie, the DVD just froze up and no matter what we tried, we couldn’t get past that scene. Now, this movie, when I burned it, didn’t give any errors. But it performed as described.
A few others, though, gave me problems while trying to burn them, making me wonder what the results will be when trying to view them.
So I figured I would use Nero CD-DVD Speed to test the burns. So far I tested a copy of The US vs. John Lennon.
Two questions: first, what does this log file from the Disc Quality test indicate to those of you who understand these things:

General Information
Drive: _NEC DVD_RW ND-3550A
Firmware: 1.06
Disc: DVD-R (TYG03)
Selected speed: 8 X
PI errors
Maximum: 1255
Average: 78.54
Total: 1169890
PI failures
Maximum: 51
Average: 0.63
Total: 5578
PO failures: n/a
Jitter: n/a
Scanning Statistics
Elapsed time: 9:53
Number of samples: 16937
Average scanning interval: 8.00 ECC
Glitches removed: 5

My other question is about the software itself. When I try and fun a few other tests that the program offers, the Start button remains greyed out, and I am unable to run the test. Any insight into this?
Thank you!

I just completed a Disc Scan on a copy of Marie Antoinette made yesterday. Please see attachment.
What can we learn from this?

DVD Scan.doc (84.5 KB)

Run the Disk Quality Test. If the score is much below 90, there could be issues with your media. Your problem could also be that you are burning right to the edge of the disk, which isn’t good either. A Quality Test will show all of that.