Requested file not found

[horst-bernd]

Hi plegall,
Can you help me with a problem? When I try to download a picture in a size that has to be generated newly, I always get a "Reqested file not found" error. When I go back and try downloading again, it works - because the picture file is than already generated. So no problem with existing picture sizes, only with new ones.
Could that be an issue of PHP version? I have 5.4 on the server.
Or may the server be to slow? So that the link to the file is generated before the picture is ready?
Many thanks for any help!