Full path and username is included (I'm guessing the person who compiled the source).

I was able to fix it by making the function static in the header file.

I moved most of my code to a library but one particular function call gives me an error when compiling.

This is the function needed for the timerAttachInterrupt():

void IRAM_ATTR TriggerTimer::cdInterrupt(){
//some codes
}

This is how I used the attachTimerInterrupt() function:

void ...