Linux client Image backup still doesn't work after update 2.5.x

Updated server to 2.5.26 and client to 2.5.19.

Client is internet client. Image backup is enabled for client (drive c = default).

Image backup says still “not supported”. Manual start does nothing.

What do I have to do to make image backups work?

If the prequisites are met already the easiest solution is to just reinstall the client and choose the wanted image backup method when asked for it.