SailfishSDK-3.7.4-windows-offline - Beginners question

Hello
could anybody help me? I installed Sailfish SDK on a Windows 10 64 bit machine. Now I would started my first step by step learning session. But if I opened a sample projekt or a new projekt I got the message “Prototype “Private.Silica.MouseArea” von “Page” could not…”". What is wrong? Since yesterday the virtuall machine runs perfekt and I can use a virtuell Sailfish phone, but it not solved the problem. Thanks in advance.

see https://forum.sailfishos.org/t/resolve-error-in-qt-creator/9889

Thanks and sorry I searched in the topics but not at qt-creator. I will try it.