The issue is the build number of the OS you're running doesn't match the build the web drivers are looking for.
Go to 'About This Mac' and click on 10.10.5 and it'll give you your build. That build number it's requesting looks like a post-security update build, so you might want to look into patching.
Thanks for the link, very good source for drivers.
Seems like what I've got is as good as it gets as for my Quadro FX 4600.
What started me searching is I inadvertently discovered that xBench video results are over twice as fast when I'm running Mavericks as they are when using Yosemite, this with the same video card on my MP 1,1.
It's not something you'd notice from day-to-day usage as I don't put a lot of demand on my systems, just sort of ticks me off as to why this is and why can't I fix it. 😡
Still fighting this nvidia web driver issue, but now it's with a Mavericks 9.5 installation.
I've solved the build version problem I was having with my Yosemite install, now the error is different, it just doesn't like my MP1,1 at all.
Same computer works fine with nividia web driver for Yosemite, WTH!
I will confess that the Mavericks default driver works pretty good already, I'm more curious then any thing else about the
latest nvidia drivers.
Open Web Driver with Flat Package Editor and copy Distribution file (just drag it) to your desktop.
Add your model name ("MacPro1,1" or "MacPro2,1") to var system_models line. Save Distribution file, delete one from Flat Package Editor and drag the one you saved/edited to it.
Thanks to all that offered suggestions my driver issues are now solved, both on Yosemite and now Mavericks.
I've updated the thread title to "Resolved" to reflect this.