Hi Gunther,
Autoload=2 will stop this happening – if you had Autoload=1 this forces the downgrade to the older firmware.
The login secreen will be caused if you have the line signon=1, change it to =0 and you will get the open desktop or G-Key the unit off the network.
To get the 5x firmware you will have to email wyse support in your area – make sure you explian what happened and provide the serial number of the unit.
I hope this helps, unfortunatly the 5 firmware is not avaliable on the public wyse site as they sell it as an upgrade now,
Cheers,
-TT