The possible cause: MagicPlotPro.exe file was moved, or the new version of the application is located in another folder. Windows stores file associations in tho steps: the name of the application (MagicPlotPro.exe) and the path to the application. Sometimes the path to the application need to be fixed manually.

Please fix the path to MagicPlotPro.exe in this Windows Registry key using regedit program: HKEY_CLASSES_ROOT\Applications\MagicPlotPro.exe\shell\open\command

Exception "java.lang.ClassNotFoundException: magicplot/*"while constructing DataFlavor for: application/x-java...

You can simply ignore these error messages. That is an old forgotten debug message that must not be visible to the end users. More information can be found here: https://bugs.openjdk.java.net/browse/JDK-6606476