Win CE 6.0 connect and disconnect

  Hello everybody, I have the following problem with my WIN CE 6.0 devices: we have a new server (windows 2012R2) with SOTI MobiControll V.14.3.3.1111 installed. It is an internal server in the closed network. Android, Win10 IoT and WinCE 6.5 are all connected and work wonderfully. The WinCE6.0 devices connect and after a few minutes they disconnect and stay disconnected until they are rebooted. in the logfile comes the following message: (0x00001090) [INFO ] [ 27] PulseChecker enter: Send: False, Check: True, Memory: 167939184, ThreadPool: 32767, 999, Queue: 0, Workers: 8 (0x00001090) [INFO ] [ 27] PulseChecker exit: Total: 22, Connected: 22, Busy: 0, Dropped: 0, Retried: 0, finished in 0 ms (0x000003e4) [INFO ] <165> Comm.Client.166171: Accepted a new connection from [::ffff:192.xxx.xxx.121]:49161. (0x000003e4) [INFO ] <165> Comm.Client.166172: Accepted a new connection from [::ffff:192.xxx.xxx.212]:53569. (0x000003e4) [WARN ] <165> Comm.Client.166172: Certificate validation failed. SSL Policy Error: RemoteCertificateChainErrors. Status: PartialChain. On the old server (Win 2008R2), everything worked fine with version 13 of Soti MobiControll. Can someone tell me why this could be and what I can do about it? greetings Georg