We just had a situation where a sales order that was invoiced earlier in the day, and pre-authorized in S/O Invoice Entry, is yielding ""Unable to communicate with Sage Exchange"" when trying to process/post-auth/post the invoice. We do see the pre-auth in VT though. Ended up not processing the post-auth from within Sage 100, and instead did it directly in VT - and then obviously had to post a Cash Receipt for the invoice balance.
It seems as if that error message points to some missing/incomplete information somewhere while Sage 100 is trying to communicate with Sage Exchange although that doesn't necessarily quite make sense since they had pre-authorized that card/invoice earlier no problem. I wonder if pre-authorizing in S/O Invoice Entry and not S/O Entry, had anything to do with it.