mirc script lines max out at around 940 characters
Also variables, hashtable items (non binary) I assume do also (more likely becuase you cant get them in and out at any larger size than they actually error)

I would assume your addtok failed.

* the 940 (aprox) is a accumulitive effect of the variable name and the value so if you have a big variable name you cant have as much data in it.