Yep, WebAssist and Adobe really need to get together and figure out the issues with the cache file being broken ALL the time. Every time that I have attempted to make use of these products this seems to be the major stumbling block that throws the proverbial wrench into the works.
Please, please, please address this issue, it is not OK (at all) for me to have to stop work to clean out a bleeding cache every time I want to use these products together.
That said: DO NOT run Digital File Pro and Universal Email 4 on the same system - there is no need for Digital File Pro (UE4 does it all now.) That should be said on a sticky at the top of both of the forums - as that would stop a lot of these issues as well.