[horde] Problem with authenticating for calendar by "Subscription URL"

[Wojtek]

I got my horde running, now I'd like to synchronize calendar, but I 
can't get to it because authentication fails.

When I use subscription URL it asks me for credentials but every time 
authentication fails. I tried to change the authentication method, at 
first I had IMAP authentication, then I changed to APP IMP 
authentication and it still doesn't work -anyway I can log into horde 
and IMP without any problem in both cases.

I tried to find some logs, but I couldn't, does anybody have an idea 
what may I be doing wrong?