SierraWhiskey:
Now I ran into a problem which doesn't mean anything to me...core.a(HardwareSerial.cpp.o): In function
global constructors keyed to rx_buffer': /opt/arduino-1.0.3/hardware/arduino/cores/arduino/HardwareSerial.cpp:515: multiple definition of__vector_55'
UxV_CS.cpp.o:/opt/arduino-1.0.3/UxV_CS.ino:79: first defined hereThis is way out of my league... What do I do now?
Maybe the same header file is getting included twice. I'm not familiar with FastSerial or Arduino in general, yet, but in all other kinds of projects we avoid including the headers twice by adding some macro definition in the beginning of the said header file.
For example, picked this for LiquidCrystal library:
#ifndef LiquidCrystal_I2C_h
#define LiquidCrystal_I2C_h
...
#endif
So, at the start of your library header file, it should say something like that, but using some other unique string in place of LiquidCrystal_I2C_h. Same goes for other header files, and they should also have their own unique id strings. And the header file should end with #endif on a new line. This avoid duplicate inclusion.
Not seeing the rest of your code, I'm assuming something like this has happened here.