I'm a french developer, I don't know if this is too late for my reply but I found the solution.
You have to change your task scheduler configuration. In action > Program / Script enter your application FMP12 path (and not the file path. ex : C:\Program Files (x86)\FileMaker\FileMaker Pro 12 Advanced\FileMaker Pro 12 Advanced.exe).
In Action > Argument enter your file path (ex : C:\myfile.fmp12).