do you have THAT specific .dll in the SAME library where RESYNTESIZER.exe plug-in is?

I had another issue similar (somehow involved PSPI). GIMP itself said I was missing a DLL that was needed by Cairo. I just ended up re-installing GIMP (not un-installing/re-installing; just installed on top of my current GIMP) and all was well.

This is an error, which regards to the kind of c++ compiler used.
It is the way the compiler handles jumps after an exception error. There are more ways:

64bit:
1. Short Jump - Long Jump - abbr.: sjlj - The older way.
2. Stuctured Eception Handling - abbr.: seh - the modern way
3. ...

32bit:
1. Short Jump - Long Jump - abbr.: sjlj
2. Dwarf2 - abbr.: dw2
3. ??? - abbr.: v0
4. ...

I do not know, how they all work, but the problem is, that some of the mechanism of that handling is in the
most basic part of the runtime: the libstdc++-6.dll. So if any program is compiled with the c++ library as an dependency,
that program demands the appropiate version of libstdc++-6.dll. This has something to do with the libgcc_s_xxxxx.dll, but the
correct function must exist in the libstdc++-6.dll.
The above error message says, that the program resynth.exe was compiled with the sjlj compiler (look at the 'sj0').
The libstdc++-6.dll that is present, uses the other way.
I do not know a way to mix both of the libraries. The official gimp team changed the compiler from sjlj to seh, I think with 2.8.10.
Then I had those problems, too. I had to change my compiler also to eliminate those errors (64bit).
From my point of view, you need a resynth.exe, that is compiled with the correct libstdc++-6.dll or try to use a different libstdc++-6.dll.
I propose to use the program called "dependency walker", there you can load an .exe or .dll file and see the dependencys.
There you can find, which dll is used, which one needs which libstdc++-6.

Hatti

I have 2 versions too conbagui but they are named in such away as to not interfere with each other. One's the new version that works with python. The old one does not. I keep the old one since it's behavior's different then the new and for certain situations, I like the result of the old over the new.

I had the problem entry point not found separate.exe and it persisted over reinstalls and even upgrades. What worked was deleting the gimp2 directory and doing a fresh install.