Error: Could not upload file

Hi,

I am trying to upload the extension Custom Image Title and get this error while uploading:

Could not upload file /webspace/xy/xyxy/domain.de/system/upload/temp-93941e2be47127c377c3a475e6e2c9c8/upload/admin/view/stylesheet/cit/css/custom.min.css

I can actually see it on the server at that place ...