FTP access blocked on specific user

[Jos Chrispijn]

I have a sudden issue connecting with a certain username on sftp and 
predefined port.

Any other user gets immidiately access on the same ip and portnumber, 
but on this specific user things get stuck:
Get a timeout and session is terminated. Only ftp:21 works.

First I thought it was domainname / dns related so I tried to get sftp 
access on internal network / ip number levelinstead of domain name. 
Unfortunately that doesn't provide access result.

Could it be that I should flush a certain session file in order to 
remove any information that blocks sftp access?

Perhaps this 'blocked user' has a damages user directory (folder) that 
causes the timeout?

Also checked ipfw icw SSHGuard (table22) but after flushing no 
improvement yet.

Can someone tell me what I may oversee here? Thanks!

/Jos