Still no success / answer
* What I did so far: renamed the Configuration folder so that it could be re-created from scratch
* removed every single extension with Extension Manager
* Installed Design Extender
* After this I installed Databridge
* After this Ecart6
* Free Tools (version 1.0.9)
(always restart, wait for download, setting up, closing DW, restart it, open php file, firing up one extension after the other, entering activation key.)
* Time spent so far: 11:25 to 13:22
* Installed DMXzone PrintIt - opened DW, put serial, registration went OK, Everything looked fine
* Installed DMXZone MultiUploader, same procedure, everything worked fine
* Installed DMXZone PurePHP Upload3 - SAME ERROR AS BEFORE (see attachment)
This is just bad service. You should be able to reproduce the errors from your clients and test them on your machines before you give such a time-consuming non-working advice. Needless to say that all the finetunings of my original configuration folder have disappeared and needs tweaking again, a process which had taken weeks and months because it was done step-by-step. This is not always bad, because you can also get rid of stuff which is no longer needed, but I had expected that I COULD GO ON WORKING ON MY CLIENT'S PROJECTS INSTEAD OF REPAIRING MY TOOLS!!!
-------------------- update ------------------------------------------
I was renaming the two files to:
in the Command subdirectory. It did not make any difference. PurePHP Upload3 would not complete the installation with the same error message I posted here. After several starts it seems it was enough to have those files renamed. Strange that they even existed. I understood that these files cause the problems and that all DA Extensions except Design Extender would remove them. Anyway. It seems it is finally working, but I am not hrough all my installation procedures.