What is a (Null) disk and why does Parallels keep asking for it?

I am upgrading my Parallels to 4.0. I get to the point where is starts to install then I get a pop up screen which says: Insert the "(null)" disc to continue the installation. Ok, I downloaded the upgrade so I dont have a disc. And nowhere in the pdf, or on their website or on this forum did I find any reference to a (null) disc. So what is it and why does my parallels want it to complete the installation? Is it possibly wanting the Windows disk?

1. Mac OS Version 10.6
2. Parallels Build # (Upgrading to 4.0 - previous version 2.5 I think)
3. What kind of computer: Intel Mac Dual-Core Intel Xeon
4. Total Physical RAM: 1 TB
5. Hard Drives: 4 (only installing parallels to main HD)
6. If you are using a BootCamp configuration or not: I have bootcamp installed but it worked fine with my previous version of parallels.
7. Did you upgrade from a BETA: No
8. With what Build did the problem start: With this attempt to upgrade
9. If Parallels Tools are installed: Dont know the installation was supposed to uninstall my old one.
10. Anything you have tried to get things working: Have looked for all previous Parallels on my comp but cant find the old version anymore (can only assume v4 removed it)
11. Anything specific about your set-up you think we should know

13. If you are getting an error message type it in and then attach a screenshot.
Insert the "(null)" disc to continue the installation


Please help. I know this has probably a real simple answer but atm I am just ripping my hair out.

 

I wanted to add, at this point I have tried both the Windows disk and my original Parallels for mac disk and neither of these seem to fill the (null) void that the program keeps looking for. I also noticed when i start to install from their download I get a conflicting virtual machine message:

"To continue the installation, shut down all virtual machines that are running or suspended and close parallels desktop and the related applications." At which point it gives me a list of my prior virtual machines. But this is the funny part. The error goes away when I close the Parallels 4.0 installer and then continues the installation as if it had no problem. I am not sure if this is what is leading to my later (null) disc issue. (See attached pics)

Error message


Once I eject the red parallels installation at which point the "continue" button becomes clickable even though I have done nothing to my other VMs that they listed.


At which point it jumps fast through prep, dest select, and install type... no problems and once I try to install.. again looking for the null disk.

The build I am attempting to install is Build 4.0.3846.

 

OK wanted to respond here because I solved the problem (it was literally the last post I submitted for error messages that was causing the issues). I had upgraded to the new OS before uninstalling the old Parallels and in doing so had no way of getting the Old version to open so i could shut down the two VMs I had created. After searching the conflicting issue I found this page. http://kb.parallels.com/en/5999. It told me to go into terminal and manually kill the old VMs. Once I did that. The (null) disc error no longer showed up and Parallels 4.0 installed fine.

 

I had the exact same problem. Normally, when I install new update software, a window pops up telling me to shut down the program that I'm updating. When the latest Parallels update popped up, it did close down my Windows VM, but the basic Parallels program (with the light under it on the Dock) was still active. A short while later, the 'nul' window popped up. I backed out of it, rebooted my computer in OS-X, made sure the 'light' was now out, and then clicked on the installation file again. This time it rapidly raced through to the point where it locked up and then continued to complete the update. EOS