ok, after upgrading to rev 7995 (and thereby replacing all files...) those errors are partly gone:
1a and b) files smaller than cpg's "Max width or height for uploaded pictures" (which at the same time represents about my servers mem limit) get uploaded withouth difficulties -- looks really smooth the way this new dialogue works! No difference between users an admin detectable
2) However, pictures larger than cpg's "Max width or height for uploaded pictures" behave strangely
a) Admin: gets the error "Fatal error: Allowed memory size of 41943040 bytes exhausted (tried to allocate 2333 bytes) in .../include/picmgmt.inc.php on line 439"
This error obviously comes from my server, who tried to generate normals and thumbs, and couldn't do so due to mem limitations.
The file gets uploaded anyhow, only the normal/thumbs are not generated.
b) Users: get an undescript errror, looks like my Error No. 2 from the initial post. Files are uploaded as well. So probably the same thing is going on, only the error message is different.
Normally I would expect cpg to suppress uploading of these files in the first instance, as they are larger than the specified maxsize? Wouldn't it be possible for cpg to inspect the the pictures file header, in order to detect its pixel size and potentially refuse pictures larger than specified by the "Max width or height for uploaded pictures" setting BEFORE uploading?
Furthermore, this leaves me now with pictures uploaded to my server that never made it into the database. Is there any way I can identify those pictures in order to delete them?
@JUpload: Thanks a lot for the hint -- I wasn't aware that it has been ported to 1.5. I always used this page
http://coppermine-gallery.net/plugins.php?cpg_version=both&sort=category&submit=#start to control for 1.5.x compatibility, where it is still (as well as addfav) falsely marked as only available for 1.4.x .
I like the touch and feel of the new upload dialogue a lot. For future development it would be great if this dialogue was able to downscale pictres that are to large for the servers mem-limits (i.e. offer the functionality JUpload is offering).
Thanks so much for your repeated help, André!!!