First, make sure you have Adobe Acrobat reader installed. You can get this from adobe's website at www.adobe.com.
If you are sure that you have Acrobat reader installed, the most common reason for this problem is that Adobe Acrobat has crashed and remains as a "zombie" in your computer's memory.
While it is a globally standard program, Acrobat reader is also unfortunately very crash-prone. The way that it crashes basically is that when you try to start it up again after a crash, nothing happens.
The easiest way to fix this is to reboot and try again.
Another way is to press control-alt-delete to get to your windows task manager. Click on the "processes" tab and select the "acroread.exe" (or whatever acrobat happens to be named - it might be "acrobat.exe" or similar) process and end it. Please note that this is for expert users only.
Unfortunately, there is not much we can do to solve this problem. Acrobat is not our product, though it is a globally standard one that our software works with.
If this does not seem to be the cause of your problem, please try re-installing the SimPlates from the original discs.
Please also understand that while we undersand that you may be frustrated because of this a) this problem was not caused by us and b) you had ample opportunity to try the DEMO version of SimPlates BEFORE you purchased and ask us about any technical problems you had with it (since it uses 100% the same technology as the purhcased version). The vast majority of users do not experience this problem. Again, this is due to some quirk in Adobe Acrobat and your system, not SimPlates.