Failed to establish connection (sometimes)

CB_Onyx

Hi,

I have a client PC which sometimes gets the message "failed to establish connection"
It's a AX40 SP1 installation, with the AOS in a hosting centre. (AOS is member of the domain)
The local network is connected through a vpn tunnel, so the users don't have to use a vpn-connection themselves.
half of the time it's no problem login in, but the other half it gets the error.
but i know the config is right.
i can ping the AOS server.

Deleted the local cache file (local settings...), and he could connect.
but i don't think this is the answer.
before Ax40 they had NO problems with AX30 SP5..was setup the same way in a hosting centre.

so..failed to establish connection..SOMETIMES !!...help ?