Do you have any log information with the "Wrong Remote Address" error? Please post it if you do.
Can you lower the encryption level? I noticed that on the snapgear the IPSec settings had encryption set at 1042bit.
Try dropping it to 256bit encryption - the more encryption the more bandwidth required and this might be a critical cause to your problem - the link between sites may be less than ideal.
IPSec is not entirely difficult - what is the username you are using to establish the VPN. Is the snapgear using RADIUS or AD or a local security (SAM). ???
It is starting to get to a point where I would try a different device, or perhaps even flash the firmware (again if you have already done so).
Has the user been configured for remote access?