FireFlyer

That worked. Thank you so much. I really appreciate all the work you guys put into this project.

Just to confirm that you mean FSUIPC6.exe? If so, no, I can not find that application installed. Only Install_FSUIPC6.exe and UninstallFSUIPC6.exe. These I can run by double clicking on them. And by following the instructions in that window to install eventually takes me to the registration screen where I enter the information, press "Register", and get the pop up error message. The only FSUICP window I can access is through the P3D program's Add-on menu which gives all the information and logging options in the unregistered version. I uninstalled the VC++ 2015, and reinstalled x64 and x86 packages as suggested. Re-ran Install_FSUIPC6.exe, entered the information, and still received the same pop up registration details not valid message.

Yes, after clicking on the Register button, a pop up window appeared with the message "Registration details for FSUIPC6 not valid - please re-enter and try again" along with the recommendation to copy and paste to ensure that the information entered is exactly as what was provided in the confirmation email.

Hello, Last night (Mar 3rd local) I purchased FSUIPC6 to use with P3Dv4.5 from simMarket, order #2668065. After re running the installation and entering the registration information, it continues to give me an error "Registration details for FSUIPC6 not valid - please re-enter and try again." - installed FSUIPC6 v6.0.12, downloaded from the website and from the simMarket email. - FSUIPC was installed in the Documents/Prepar3D v4 Add-ons folder. Other locations were tried as well but still yielded the same results. Complete uninstall was done from each location. - All 3 fields (name, email and key) were entered multiple times by both typing manually and by copy-and-pasting to ensure they were correct as provided. (WideFS Key was left blank as this was not purchased). - FSUIPC appears to be running fine unregistered in Prepar3D as it shows in the add-on menu and its window opens when selected. - The provided documentation mentioned checking the computer system's date and time as this was said to cause problems. As the purchase was made late at night (just before midnight) I didn't know if that could have an effect. In the end the system time checks ok. Would there be anything else I could try to get it working. Thanks.