LMS 7.7.3 problem firmware upgrade squeezebox

Hi,
I do have a LMS 7.7.3 running on a synology server.
Works perfectly with a downgraded sqeezebox UE.

Now I got a squeezebox (3) that connects well to the server and starts to upgrade the firmware.
After 2/3 progress I alwasy get the message "nb alloc failed in slimproto"
The squeezebox is on firmware 88 and runs well with mysqueezebox.com.

Any ideas?

Thanks for any suggestions
Ralf