C++ using Boost with unsigned char*

[Lindley]

Casting the result of c_str() to a char* (essentially casting away const-ness) is a bit dangerous. If you're absolutely certain that the decode() method doesn't change its argument, you should make it accept a const char*; otherwise, you need to pass a modifiable char array, which the result of c_str() is not.

(This will change in the next standard version, but holds for now.)

However, that probably isn't your problem here. One thing you could try is try outputting fullPath.length() in your debug statements, to catch if any whitespace characters have gotten in there somehow.