Because I got the UI error message over and over again, I decided to reinstall Avast Free.
I Used the Offline Installer 17.8.2318, after which everything worked fine, and I could open the User Interface and see its version.
After a while Avast Free found it could be updated and did this to the actual version 18.5.2342.
Even after that update I still could open the User Interface and see it was updated to the new version.
During aal this tine I always see the service AvastSvc.exe running.
After a while Avast asked to reboot the system, or postpone the request for 10 minutes.
As long as the reboot was postponed, I could open the User Interface without problem.
However after reboot I get the an AvastUI error window telling
UI Failed to Load
This is really embarassing
AV Service is not responding
Exit or Restart Service.
As this happens the service AvastSvc.exe is gone.
After restarting the service by this means (AvastUI error window)I see AvastSvc.exe for a while, and then the service(process) exits and I get again that AvastUI error window.
Why everyting (AvastSvc.exe) seemed to work before the (mandatory) reboot, and not any more after?
This is the AvastSc.log file after each restart of the service.
It seems the error " failed to connect to service controller" is the reason why the service exits.
NB. Background Intelligent Transfer Service is always running.
[2018-07-19 09:07:15.531] [info ] [settings ] [ 3240: 3252] paths.ini_store configuration is empty, settings ini store folder to asw::instup::GetDataDirectory.
[2018-07-19 09:07:45.171] [info ] [svcmain ] [ 3240: 3252] Installing CrashGuard global exception handler...
[2018-07-19 09:07:45.171] [info ] [crashguard ] [ 3240: 3252] CrashGuard global exception handler installed
[2018-07-19 09:07:45.171] [info ] [crashguard ] [ 3240: 3252] CrashGuard initialized successfully, external dumping enabled
[2018-07-19 09:07:45.171] [info ] [crashguard ] [ 3240: 3252] Crash handler installed successfully process-wide from module 4194304
[2018-07-19 09:07:45.171] [info ] [svcmain ] [ 3240: 3252] Service starting up.
[2018-07-19 09:07:45.281] [info ] [base_init ] [ 3240: 3252] Entering basInitLibrary...
[2018-07-19 09:07:45.281] [info ] [base_init ] [ 3240: 3252] Calling cmnbInit...
[2018-07-19 09:07:45.281] [info ] [base_init ] [ 3240: 3252] Calling CrashHandlerInstall...
[2018-07-19 09:07:45.296] [info ] [crashguard ] [ 3240: 3252] Crash handler is already resident in this process. Enabling only manual dumping from this binary.
[2018-07-19 09:07:45.312] [info ] [crashguard ] [ 3240: 3252] CrashGuard initialized successfully, external dumping enabled
[2018-07-19 09:07:45.312] [info ] [base_init ] [ 3240: 3252] Validating paths...
[2018-07-19 09:07:45.312] [info ] [base_init ] [ 3240: 3252] Initializing languages - getting ini...
[2018-07-19 09:07:45.312] [info ] [base_init ] [ 3240: 3252] Initializing languages - GetLocaleInfo...
[2018-07-19 09:07:45.312] [info ] [base_init ] [ 3240: 3252] Initializing languages - basCreateLanguagePath...
[2018-07-19 09:07:45.312] [info ] [base_init ] [ 3240: 3252] Initializing languages - basInitThreadLocale...
[2018-07-19 09:07:45.312] [info ] [base_init ] [ 3240: 3252] Initializing language paths...
[2018-07-19 09:07:45.343] [info ] [base_init ] [ 3240: 3252] Loading Base.dll...
[2018-07-19 09:07:45.359] [info ] [base_init ] [ 3240: 3252] Calling GetComputerName...
[2018-07-19 09:07:45.359] [info ] [base_init ] [ 3240: 3252] Calling InitTCPIP...
[2018-07-19 09:07:45.375] [info ] [base_init ] [ 3240: 3252] Calling InitSound...
[2018-07-19 09:07:45.375] [info ] [base_init ] [ 3240: 3252] Leaving basInitLibrary...
[2018-07-19 09:07:45.375] [error ] [serviceapp ] [ 3240: 3252] failed to connect to service controller
[2018-07-19 09:07:45.375] [info ] [svcmain ] [ 3240: 3252] Service shut down completely.
[2018-07-19 09:07:45.375] [info ] [settings ] [ 3240: 4028] WatchThread termination requested via IDX_TERMINATE.
[2018-07-19 09:07:45.375] [info ] [settings ] [ 3240: 4028] WatchThread gracefully terminated.