How large is the SSD? 120 GB
How much free space is on the SSD? 38 GB
I think Parallels is about 425 MB. Is /Applications on the SSD? yes
You are saying /Users is on a 2nd disk? How did you set that up? doing a right click on on user name in accounts system pane logged in as another user, then change user's home directory to 2nd disk. I only change location of that user (I do this to every user on boot disk). Very handy if you blow up your computer on a regular basis, just install OS and apps and away you go (I make a disk image of boot drive) , no need to copy data, and if you kill the user library (which I do) you have an instant clean install with all data intact.
can I install parallels to run with all users? that might solve all problems
Could you put /Users back on the SSD (without your user files) and try installing again? i can create new user. changing user information (after account is active and being used) is bound to become a problem down the line.
How big is the 2nd hard drive? 2 TB
Is it big enough for a 2nd installation of Mac OS X? I thought of that, can't boot to 2nd drive because I use the same path as the 'normal' users on boot disk, permissions would quickly become a problem. You could install Mac OS X to a new partition on the 2nd disk (shrink the existing partition). Then see if you can install Parallels to that partition. Then maybe you could move the installation to the first partition. I have third disk I can use that Is a 40 GB SSD, currently used as a scratch disk. I'll copy via Carbon Copy Cloner the boot drive and install parallels on that one if the above ideas don't pan out.