Well, i downloaded this mod and then this happened
http://prntscr.com/omavkk
Yeah i don;t know whats happening but i don;t think that;s how this mod's supposed to work.

Needs more information. BP Version? Other mods? Logs?
You might want to read this article about how to make effective bug reports.

Oddly enough it fixed itself after i restarted the game so I can't recreate it for a more detailed report.
I think I know what caused it anyways, though. Sildurs Vibrant Shaders Lite (With optifine). Lighting a portal with these shaders on will just yield a completely black portal, and the bug happened right after i turned the shaders back off.

The black portal with shaders is intentional as OF does not (and does not plan to) support rendering of multiple worlds (see CF description), so I BP intentionally disables its see-through part when shaders are active.

OF does some stuff when turning shaders on/off and I'm guessing that doesn't work with multiple worlds either.
With OF being proprietary, there's not really anything I can do about it, so I'm going to close this as not-our-bug and just add a note to the section in the CF description.