V8 PPTP clients disconnected while uploading files

Hello

i face a weird trouble.

i have two V7, on two different internet lines. PPTP worked perfectly

i upgraded those V7 to V8 (V8.308).
Since then almost everytime that a client connects on it and uploads a file on our network, the connection cuts !

have someone already seen that before, or face the same issue ?

please help !

thanks very much