Looks like non German versions of MS Windows install GNUmed into the folder C:\Program Files\GNUmed-client. The start menu entry then fails to start GNUmed because of a whitespace in the application path.
This can easily be fixed by quoting the path. Navigate to the start menu entry for GNUmed as you would left-click it to start it. Now right-click on it and choose 'Properties'. Insert two pairs of double quotation marks like in this example.
"C:\Program Files\GNUmed-client\bin\gnumed.pyw" --conf-file="C:\Program Files\GNUmed-client\gnumed.conf"
This will be fixed in the installer for the next bugfix release.