I post this in case anyone else runs into this alarm message. There is very little help I could find anywhere about what was causing the problem. I am a newbie so this was confusing to me but the old guys probably knew this information already
I got my mill used so various interesting problems have arisen that are not covered in the Fanuc manuals. This is one of them.
Alarm: 151 - TOOL GROUP NUMBER NOT FOUND
Basically, wherever a tool call was made in my program an alarm message as above appeared. I could press "reset" and continue the program but this is obviously a big inconvenience. I had to follow a search on the word "groups" and eventually I suspected a connection with the "tool-life" option in the CNC. To be breif, I found that there is a parameter in the 900 range that turns some sort of "Tool Life" tracking on. This involves the use of some value called "Tool Groups". When I turned this parameter "Off" the normal tool call in the programs ran fine.
Before you actually turn the parameter off a warning appears on the screen saying that you will lose certain files, do you wish to continue? I can tell you that continuing deletes all stored program files, it also probably deletes any tool offset and wear tables but since mine were empty I cannot confirm this. I have not found anything else that has been deleted yet, I will post immediately if I do find anything.