Unable to connect to VMware ESXi 5.0.0 (build-469512) from

I just realise that I cannot connect to my "old" Esxi 5.0.0 from vSphere Client 5.5.0

I get this error:

"vSphere Client could not connect to

An unknown connection error occurred. (The client could not send a complete request to the server...)"

What i tried:

- connect from 2 different pc (1 Win 7 64bit , 1 Win 8 Pro 64bit) --> same result

- check various KB (2011834 , 1003490 , 2030663 , 2049143) --> same result

- try a Thinapped vSphere Client (v. 5.0) --> same result

But I can connect to the server via SSH

I didn't try to restart hostd (v.  /etc/init.d/hostd restart ) because I have 4 working VM...

Thanks, Thomas