no Panadapter on Maestro-B after upgrade 3.7.4

Hi,

For various reasons, I had not used my Flex6400 and the associated Maestro-B for at least 18 months. As of 24 June, the operation of remote stations is now officially approved in Germany and I have remembered my technology.
The first thing I did was to install SmartSDR software version 3.7.4 on my PC and then update the Flex6400. This worked perfectly and I can control the transceiver from the PC. In the next step, I put the Maestro into operation and it recognised the Flex6400. The software update was also offered here and I carried it out. The update went through without any problems and at the end the Maestro rebooted.
Unfortunately, I no longer see a panadapter in the display. I can start the menu and when I press PTT on the microphone, the MOX LED lights up red. But I can neither see the waterfall nor do I have any control over the frequency. I can switch the various metres on and off, but nothing more. If I try to activate a panadapter with the small arrow at the bottom centre, I get the message:
Panadapter limit has been reached. Close a Pandapter and try again
or also
Slice limit has been reached. Close a slice an try again

In case it is important, here are the serial numbers.
Maestro: 4017-0669-0101-3347
Flex6400: 5018-6928-6400-1015 (HW v3.7.4.29165)

73s de Tor, DM1TS