since the problem did not go away, I made further testings and found the bug:
I can repeat the error message every time now under specific circumstances.
There are 3 restrictions for uploading images:
1. The image is to big in KB
2. The image is too big in size (pixel) - Max allowable image width/height in pixels = 1000
3. The image is too small in size (pixel)- Min allowable image width/height in pixels = 400
For number one there is no problem. This is what I always tested in the past. A user tries to upload an image which is too big in KB, it gets rejected and he can try with anthother one. No problems at all.
But number 2&3 are the trouble shooters. If a user is uploading an image which is too big in pixel (but KB is o.k.), he comes to the second upload screen. When he then clicks on submit, he gets rejected (which is fine), but can not upload afterwards another image.
Same procedure and consequence, if he uploads an image, which is to small in pixel (not KB). Same error message, same consequences.
So the bug is, that photopost checks always first only the KB size, not the pixel size.
If KB is correct, it seems to upload the image on the server already (not yet visible in the gallery). Only after that step it checks whether the image is too big/small in pixelsize. But this is too late.
As a result, IMHO the image is already on the server and this leads to the error that he uploaded already an image within the last 24 hours.
How can I fix this?
Thanks in advance
P.S.: 2 other minor problems for the same issue: The alert sais ALWAYS that the graphic is too small (pixel), although it is sometimes too big (pixel). So the wrong error message appears, if the image is too big.
Secondly the text is hardcoded in image-inc.php