Izotope Support responded promptly and sent me a revised build as it appears one or two other users have hit the same problem.  Unfortunately Izotope can't reproduce the issue, and sadly, the new build didn't fix things, but at least I'm not alone and they're working on it.
 
I'll post updates as and when; in case other users here encounter the same multiple error popup problem.
 

Skyline_UK
Izotope Support responded promptly and sent me a revised build as it appears one or two other users have hit the same problem.  Unfortunately Izotope can't reproduce the issue, and sadly, the new build didn't fix things, but at least I'm not alone and they're working on it.
 
I'll post updates as and when; in case other users here encounter the same multiple error popup problem.
 

Thank Sky...keep us informed...I know they'll take care of it...

Sorry to hear you are having this trouble Sky...I was going to suggest using a restore point on your DAW to eliminate a troublesome MS update that might have appeared after iZotope did final testing before release. I have upgraded last night to Ozone Advanced 64-bit, but I opted for standard install. Hope you get it sorted soon.
 
Garry Kiosk

All installed fine here, and as was mentioned above the vst3 path is an automatic thing I think the same for everyone C:\Program Files\Common Files\VST3 or something like that. If there are others in the same boat I assume they will get to the bottom of it in short order, just a matter of them working out the issue, which I am sure they will. But yeah it sucks when stuff like this happens, but one good thing, it will be worth it in the end, Ozone 7 Advanced is pretty awesome, I only joined the Izotope club back with Ozone 5, and quickly purchased all of there products that were of interest to me and never regretted a purchase. Best of luck.

Richard Cranium
All installed fine here, and as was mentioned above the vst3 path is an automatic thing I think the same for everyone C:\Program Files\Common Files\VST3 or something like that. If there are others in the same boat I assume they will get to the bottom of it in short order, just a matter of them working out the issue, which I am sure they will. But yeah it sucks when stuff like this happens, but one good thing, it will be worth it in the end, Ozone 7 Advanced is pretty awesome, I only joined the Izotope club back with Ozone 5, and quickly purchased all of there products that were of interest to me and never regretted a purchase. Best of luck.

I've got it working. But here's the interesting thing.
The default VST3 path offered by the O7 installer is a Steinberg one, which does exist on my PC, but the install exe baulked for every component, refusing to install any VST or dll files and throwing up an error popup for each one, hence the quantity.  So this morning I opened Sonar and looked to see where it was finding the Ozone 6 plugin components and it was the path you mention above, "C:\Program Files\Common Files\VST3".  So I changed the custom installer to tell it that was the location for VST3 purposes. And everything went smooth as a nut.
 
I then realised what I think is the explanation for the problem.
This was an upgrade from O6 so the installer was checking to see that I had the relevant O6 components before allowing me to install. It couldn't see them in the installer's default location so threw up all the errors. As soon as I told the installer to use "C:\Program Files\Common Files\VST3" it found the O6 stuff it was checking for and proceeded.  I don't remember installing O6 so don't know whether it was me or the O6 installer that put the O6 plugin files in that location.
 
It would have been helpful if the error popups said "Sorry, can't find previous version's components to validate this upgrade. Please check file path." But then I'm not a programmer.....
 

In reading this and several similar threads, it just amazes me the hoops users are so patiently willing to jump through in order to use VST3 plugins specifically. Seriously, why bother? If there's some problem with a product's VST3 implementation or installer, just use the VST2 version and get on enjoying your new toys.

bitflipper
In reading this and several similar threads, it just amazes me the hoops users are so patiently willing to jump through in order to use VST3 plugins specifically. Seriously, why bother? If there's some problem with a product's VST3 implementation or installer, just use the VST2 version and get on enjoying your new toys.

Yeah but Bit, VST3 is a least 'one' VST better isn't it, surely ?

The Kiosk Project
 
Yeah but Bit, VST3 is a least 'one' VST better isn't it, surely ?

hmmmm, I think it is '0.6' VST better ? wasn't VST 2 (2.4) ?

I was having the same issue... really frustrating. Glad you figured it out I will try it asap

I know this is an old post, but I encountered this problem the other day and wanted to help others that might encounter this issue.
 
It seems that is this caused by the plugin install path containing whitespace. The installer will work if it uses the 8.3 format (e.g. progra~1, instead of program files), but will otherwise interpret the path as a path with arguments (in the case of program files, it will think program is the path and files is an argument); I don't understand why sometimes it uses the 8.3 format, and the full path format at other times.
 
The solution is to install it to a path without spaces. If you want to install the VST 3 plugins only, the default location of VST 2 plugins is stored in the registry at
 
HKEY_LOCAL_MACHINE\SOFTWARE\VST
HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\VST
 
and can be modified if necessary; remember to back up the existing value(s) just in case.