Too many concatenations or variable references have been made; there are too many nested functions. Probably, somewhere you got a gosub without a return or something similar
A recursive gosub (i.e. a gosub that calls itself)
Remedy:
Break the statements and expressions into smaller, less complex pieces. Reduce the number of variables, nested functions, and gosub calls. You can also increase the RPNStack setting in the BRConfig.sys file, but remember that RPN stack space comes from user memory.
Remove the call to the gosub from within the gosub