QuickBooks dilema

Most likely what happened was that one of the PCs was allowed to contact Quickbooks for program updates.
Here's the easiest way to fix it...
Open Quickbooks
Under file Click Update (I believe that's where it is.)
Let both PCs get the most recent updates, then try.

save yourself money and time by coughing up for newer version is my 2 cents. see if this is you:
Question: After installing a new version of QuickBooks, why does an older version open when I click on the icon?

Answer: You may have multiple installations of QuickBooks on your system. To find out if you have other version(s) of QuickBooks installed:

Search the hard drive for multiple copies of QBW.EXE (QuickBooks V5.0) and QBW32.EXE (QuickBooks V6.0 and later) to identify location of other installations.

In Windows 95/98

Click Start, point to Find, and then click Files or Folders.
In the Named box, type QBW32.EXE.
In the Look in box, type the drive to which you installed your QuickBooks software (for example: C:\), click Include subfolders, and then click Find Now.
The search window should list the path to your QBW32.EXE. Write down the full path name.

Repeat for QBW.EXE
Note: We do not advise deleting the directory of the older version because your QuickBooks data files may reside there.