Here is a solution that seems to work:
1- Delete any file in this folder
C:UsersAppDataRoamingMetaQuotesWebInstallmt4clw
2- delete any file in this folder
C:ProgramDataMetaquotesWebInstall
3- If mt4 already upgraded, replace terminal.exe and metaeditor.exe with old files
4- Right click the 2 above folders, and set deny permission for everybody:

5- Launch mt4 again