Update from 18.1.36 not possible

Hello

I'm trying to do the update from 18.1.36.3733 on Win 2008R2 to an actual version of PRTG but it doesn't work.

Auto-Update: Installs the new version, looks good, it makes one or two reboots and then... back on 18.1.36.

Manual Update: After stopping the prtg core and probe service, I've tried to install the PRTG Setup (18.4.47.1962). The installation finishes without error but after a server reboot, PRTG core cannot start. The webpage shows the progress of the initialication up to 60%, then the core service stops and startup again.

Below, you'll find the prtg boot records in core.log, the thirdlast line contains a file access violation.

How could I fix this PRTG installation?

Thanks for any hints

2019-01-22 11:11:56.707429 INFO TId    1824 Core> InitBasics: Logger initialized.
2019-01-22 11:11:57.322664 INFO TId    1824 Core> Validating done
2019-01-22 11:11:57.322664 INFO TId    1824 Core> Trying to get handle
2019-01-22 11:11:57.322664 INFO TId    1824 Core> System Info obtained
2019-01-22 11:11:57.322664 INFO TId    1824 Core> Handle Obtained, Trying to get Systeminfo
2019-01-22 11:12:00.631257 INFO TId    1824 Core> PRTG Network Monitor 18.4.47.1962 
114d708d4b635b4b8863319ff147e22732ceeda4 Core Server starting on "BYCVSRV020"
2019-01-22 11:12:00.707429 INFO TId    1824 Core> Startup: OS: Microsoft Windows Server 2008 R2 Standard  (6.1 Build 7601 Service Pack 1 SPV1.0), 3 CPUs (3x x64 Model 79 Step 1), code page "Windows-1252", on HyperV
2019-01-22 11:12:00.707429 INFO TId    1824 Core> Startup: System Path: D:\Programme\PRTG Network Monitor\
2019-01-22 11:12:00.708406 INFO TId    1824 Core> Startup: Data Path: D:\Programme\PRTG Network Monitor\Data\
2019-01-22 11:12:00.708406 INFO TId    1824 Core> Startup: Formatting: dd/MM/yyyy | dddd d MMMM yyyy | hh:mm | hh:mm:ss
2019-01-22 11:12:00.708406 INFO TId    1824 Core> Probe settings: IPs: 127.0.0.1 - Port: 23560 - SSL: -1
2019-01-22 11:12:00.708406 INFO TId    1824 Core> Memory Manager: NexusMM4
2019-01-22 11:12:00.708406 INFO TId    1824 Core> libeay32.dll=1.0.2.11
2019-01-22 11:12:00.708406 INFO TId    1824 Core> System time zone: (UTC+01:00) Brussels, Copenhagen, Madrid, Paris
2019-01-22 11:12:00.708406 INFO TId    1824 Core> ssleay32.dll=1.0.2.11
2019-01-22 11:12:01.063875 INFO TId    1824 Core> LicenseInit: OK&si1=0&si2=0&si3=0&si4=0&si5=0&si6=0&si7=0&si8=0&si9=0&
si10=0&si11=0&si12=0&si13=0
2019-01-22 11:12:01.065828 INFO TId    1824 Core> PRTG Network Monitor 500 licensed for "Bouygues E&S FM Schweiz AG" (xxxxxxxx-
xxxxxxxx-xxxxxxxx-xxxxxxxx-xxxxxxxx-xxxxxxxx-xxxxxxxx-xxxxxxxx-xxxxxxxx-xxxxxxxx) Edt=70 MaxS=500, DayL=364821 DaysIn=729
2019-01-22 11:12:01.065828 INFO TId    1824 Core> SystemID: SYSTEMID-xxxxxxxx-xxxxxxxx-xxxxxxxx-xxxxxxxx-xxxxxxxx-VERSION-
18.4.47.1962
2019-01-22 11:12:01.065828 INFO TId    1824 Core> PRTG Network Monitor 18.4.47.1962 Core Server is running a license for PRTG on 
premises.
2019-01-22 11:12:01.065828 INFO TId    1824 Core> InitCore: Registering Singletons....
2019-01-22 11:12:01.065828 INFO TId    1824 Core> InitCore: Registering Singletons done.
2019-01-22 11:12:01.065828 INFO TId    1824 Core> Startup: Initializing global Threadpools
2019-01-22 11:12:01.065828 INFO TId    1824 Core> Startup : Initializing Push Manager
2019-01-22 11:12:01.065828 INFO TId    1824 Core> Startup: Reading port configuration..
2019-01-22 11:12:01.067781 WARN TId    1824 Core> CheckPortIsFree: Port 80 on 192.168.198.32 is occupied.. Waiting, retrying.. 
2019-01-22 11:12:03.068757 WARN TId    1824 Core> CheckPortIsFree: Port 80 on 10.10.18.138 is occupied.. Waiting, retrying.. 
2019-01-22 11:12:05.069734 WARN TId    1824 Core> CheckPortIsFree: Port 80 on 127.0.0.1 is occupied.. Waiting, retrying.. 
2019-01-22 11:12:07.071687 INFO TId    1824 Core> Startup: Starting webserver...
2019-01-22 11:12:08.129304 INFO TId    1824 Core> Startup: Started webserver for IPs:Ports 192.168.198.32:443,10.10.18.138:443,127.0.0.1:443,127.0.0.1:8085 (URL: http://192.168.198.32:443)
2019-01-22 11:12:08.129304 INFO TId    1824 Core> Port Mode: SSL - Port Security: inactive - IP Mode: AllIPs
2019-01-22 11:12:08.130281 INFO TId    3480 Core> Startup: Loading Configuration File: D:\Programme\PRTG Network Monitor\Data\PRTG Configuration.dat
2019-01-22 11:12:36.934206 INFO TId    3480 Core> Load Done
2019-01-22 11:12:36.934206 INFO TId    3480 Core> Update 1
2019-01-22 11:12:37.069940 FATL TId    3480 Core> Startup: Loading Configuration File: Error (Access violation at address CCFFD387 in 
module 'PRTG Server.exe'. Execution of address CCFFD387)
2019-01-22 11:12:37.072869 INFO TId    1824 Core> Stop Done
2019-01-22 11:12:39.210428 INFO TId    1824 Core> System Cleanup Done