Can someone tell me how to fix this error in 10.4.11 on a G5 Quad Core 2.5GHz Tower...A valid video device could not be found for playback. [-70017]

It would help to know what you're trying to do when you get that message. Divining something from nothing isn't the forté of anyone here as far as I know. A screen shot would also help.

In other words, we need more details than what you've given us.

That's an error reported from DVD Player I believe...

kDVDErrorMissingGraphicsDevice = -70017, // A valid graphics device is not available.

There's some conjecture it has to do with HDCP, or Video Card problems, but the only 2 cures/fixes I found were Software related, one was cured by updating the OS, another by replacing the Video kexts.

I think this error also shows up if trying to use DVD player in Safe Mode, (too much research isn't good! 😉 ).

At the Apple Icon at top left>About this Mac.

Then click on More Info>Hardware>Graphics/Displays and report like this...

NVIDIA GeForce 7800GT:

Chipset Model: GeForce 7800GT

Type: Display

Bus: PCI

Slot: SLOT-1

VRAM (Total): 256 MB

Vendor: nVIDIA (0x10de)

Device ID: 0x0092

Revision ID: 0x00a1

ROM Revision: 2152.2

Displays:

VGA Display:

Resolution: 1920 x 1080 @ 60 Hz

Depth: 32-bit Color

Core Image: Supported

Main Display: Yes

Mirror: Off

Online: Yes

Quartz Extreme: Supported

Display:

Status: No display connected

Can't think of much to try at the moment, but perhaps reapplying the big 10.4.11 combo, Repair Permissions, & reboot would help, not sure. 🙂

The combo update for PowerPC-based Macs...

http://www.apple.com/support/downloads/macosx10411comboupdateppc.html

Also, if you're trying to use it from an external DVD Player...

DVD Player doesn't like external players, use VLC Player...

http://www.videolan.org/vlc/

Great to hear, thanks! 🙂