Please follow this workaround in the case if the installation process hangs on creation of Directory Cache database. Unfortunately, there is a conception problem with upgrades from older versions, because of changes in db.dll.Directory Cache is populated before the installation starts therefore it uses the old db.dll instead of the new one.

Workaround:
1. obtain new db.dll from the installer - links are bellow. If you are going to upgrade your server to 32-bit IceWarp Server 10.4.5 download db.dll-icewarp10.4.5-32bit.zip, if to IceWarp Server 64-bit download db.dll-icewarp10.4.5-64bit.
2.stop all services
3. backup db.dll, replace it with the new one
4. start the installer, let the Directory Cache population start
5. do not wait for the population to be finished
6. restore the original db.dll (only the installer is going to use the new dll)
7. start all services.

Optionally, you can skip steps 2 and 7 (because dll can be renamed even if it is used)