ip overlap

An overlapping network (subnet) is when you establish a connection from the VPN client to another network with the same ‘private IP address range’, and an ‘overlap’ occurs with the addresses.  I.e. the hotel router assigns your machine a ‘private IP address range’, i.e. 192.168.1.0, and this address matches the office’s.  When the client connects, it uses the source IP address it currently has, which is the home network.  The gateway sees this as an internal (local) address, and thus networks overlap and deny your VPN connection.