Get rebar.dll from
here. Although this is still version 0.2, it appears to be a later build, one that supports 6.14. There's gonna be a problem in the next version though, until the author updates the dll again: if you take a look at the source code (rebar.cpp) of the latest build, you'll see that it supports mirc versions 6.1 to 6.14. The fix is easy though; you would only need to change 1 byte from the dll with a hex editor, something that can be done with a simple /bwrite (since the dll is open source, I doubt that the author would mind if you edited the binary for personal use). Of course, if you have and know how to use a compiler, you can edit rebar.cpp, change 6.14 to the new mirc version and compile it.