Following behavior now:

Starting from Ambient:

ShowCRexx opens window, a pic can be dropped in. Clicking double Pic-name (or once and button "start") loads the pic into seperate window and gives Error Invalid argumentation to function: line 8

Starting from Shell rx ShowCRexx.rexx does the same,but with no Error. The converted (50%size) pic is shown in seperate window, but not stored anywhere (should be in RAM, or?). Shell gives following information:

Ram Disk:ShowCRexx> rx ShowCRexx.rexx
DROPLIST0 Download:b2,jpg
[CLI 7]
ram:heightwidth Deleted
oto sort Sliders(%)
+++ Error 18 in line 333: Invalid argument to function
+++ Error 18 in line 276: Invalid argument to function
+++ Error 18 in line 24: Invalid argument to function
+++ Error 18 in line 8: Invalid argument to function
Command returned 10/18: <This space intentionally left blank!>

Whats wrong?