Thank you for reply.
I've tried now the rewrite rule, but I've still the same error.
I've checked again my log files from apache and find out, that the problem is, that the authorization was lost.
Code:
87.138.86.47 - mossi [26/Sep/2013:11:10:54 +0000] "GET / HTTP/1.1" 200 2881
87.138.86.47 - - [26/Sep/2013:11:10:54 +0000] "GET /mobile/style.css HTTP/1.1" 401 636
87.138.86.47 - - [26/Sep/2013:11:10:54 +0000] "GET /static/calibre.png HTTP/1.1" 401 636
87.138.86.47 - - [26/Sep/2013:11:10:54 +0000] "GET /get/thumb/4480 HTTP/1.1" 401 635
87.138.86.47 - - [26/Sep/2013:11:10:54 +0000] "GET /get/thumb/4479 HTTP/1.1" 401 636
87.138.86.47 - - [26/Sep/2013:11:10:54 +0000] "GET /get/thumb/4478 HTTP/1.1" 401 636
As you can see, the first GET uses the username "mossi", but the following requests do not use any username.
I think, this a problem with my apache configuration, but I have no idea why this is happening only with this site.
off: I changed authorization to basic auth because of this problem. I already changed it back to digest mode.
edit: I tested now with my PRS-T2 and I there is a similar problem. The images are shown here, but when downloading an EPUB, Ive got the same error.