Version:            (using KDE Devel)
Installed from:    Compiled sources

Summarised from a user on IRC:

Apparently official clients restrict password length to 8 chars.  
Kopete's ICQ UI allows passwords with more than 8 chars but cannot login with them.  
Licq allows passwords with >8 chars and can log in.

Looks like licq allows you to enter a long password but truncates it to 8 chars internally.

Will

jens_> Hi everybody ... it seems I solvd my problem not being able to connect. The password was longer than 8 characters...
<jens_> can somebody please try to page me #47505749 ? just for testing
<Bille> jens_: ICQ?
<jens_> Bille : yep.
<jens_> (I forgot that kopete is so flexible ;)
<Bille> you're online...
<Bille> so is a long password illegal?
<jens_> apparently. I just installed the windows 2003 version and it beeps if you want to enter a 9th character in the password field.
<Bille> how did you set a long password in the first place?
<jens_> Bille : with licq ;)
<jens_> (I think... was a LONG time ago, I started using ICQ in 1998 or something)
<Bille> and you could authenticate with licq with a long password?
<jens_> Bille : yes, until about 3 months ago. then licq started choking with some weird errors, which is why I looked for alternatives
<jens_> but it seems licq wasn't to blame at all
<jens_> ;)
<Bille> were the licq errors to do with the password or just unrelated problems?
<jens_> the licq errors were the ones detailed here: http://www.mail-archive.com/licq-devel@lists.sourceforge.net/msg01767.html
<jens_> different hex dump but same error (at 23:48:24)
<Bille> hmm maybe ICQ changed their authentication so long passwords no longer worked - but then how were you able to change your password?  Or did you just get a new ICQ account, your UIN is pretty big if you started in 1998...
<jens_> no, I just cropped my password to 8 chars. that worked. maybe the other clients do that as well.