These are just total shots in the dark -
Make sure there's only one copy of the program file on your hard drive, by searching the drive for "Pentagon I.dll".
The other thing is to check the version. There's a discrepancy on my machine between the version number that appears from within Pentagon and the number that is given in the file properties. I'm using Win 7, so I don't know how this works in Win8, but find the dll on your hard drive, click on the properties, and then on the "Details" tab to find the version number. On my installation (which works fine), it is 1.5.0.0. Strangely, if I check the version from within Pentagon, it is 1.4 - I'm assuming there was an oversight somewhere along the line.
Finally, there's another little dll that accompanies the main one. I don't know what it does, but it's there in the same folder. It's "P1DXi.dll". You might want to check to see if it is there on your system.