> In the file htsglobal.h, I have just changed :
> #define HTS_URLMAXSIZE 512
> by
> #define HTS_URLMAXSIZE 1024
> But it doesn't work. Why ?
Strange?!

> (You can see some lines of the error log at the end 
of 
> the mail). 
> 10:32:21 Error:  'Proxy Error ( Host konnte nicht 
> gefunden werden )' (502) after 2 retries at link 

Hum, the error is related to your proxy, not the URLs 
size:
HTTP error 502='Bad Gateway'

You may need creditentials to access to the proxy?(user:pass@proxy:port)