Trouble using Kevin Watson's Serial Code with Vex user API

[StargateFan]

Hi,
I am trying to link the user API supplied with the Vex programming kit to a project using Kevin Watson's serial drivers. In particular, I want the program to receive data through the serial port and then move a servo. I have code that receives data through the serial port but when I tried to add a SetServo() call from the user API, I got a linking error. I linked user_api.o to the project and the error message I received was:

MPLINK 3.90, Linker
Copyright (c) 2004 Microchip Technology Inc.
Error - could not find definition of symbol 'EnableInterrupt' in file './user_api.o'.
Errors : 1

So then I linked interrupts.o (also supplied by Vex) to the project and I received this error message:

MPLINK 3.90, Linker
Copyright (c) 2004 Microchip Technology Inc.
Error - could not find definition of symbol 'Old_Port_B' in file './interrupts.o'.
Errors : 1

Then I tried linking the only other .o file supplied by Vex that didn't correspond to any of Kevin's serial port code - Start.o. But once again I received an error:

MPLINK 3.90, Linker
Copyright (c) 2004 Microchip Technology Inc.
Error - symbol 'txdata' has multiple definitions.
Errors : 1

I have no idea how these files supplied by Vex are implemented since I only have the '.o' files (in the case of user_api.o, I also have a header file but this only contains function protoypes). Has anyone else tried to use the vex user API in this way? Any help would be greatly appreciated.

Thanks.