HP 15c - Manual (Page 207)

Appendix A: Error Conditions 207
Error 3: Improper Register Number or Matrix Element
Storage register named is nonexistent or matrix element indicated is
nonexistent.
Error 4: Improper Line Number or Label Call
Line number called for is currently unoccupied or nonexistent (>448); or
you have attempted to load a program line without available space; or the
label called does not exist; or User mode is on and you did not press ´
before ¤, ', @, y or ∕.
Error 5: Subroutine Level Too Deep
Subroutine nested more than seven deep.
Error 6: Improper Flag Number
Attempted a flag number >9.
Error 7: Recursive
_
or
f
A subroutine which is called by _ also contains a _ instruction;
a subroutine which is called by f also contains an f instruction.
Error 8: No Root
_ unable to find a root using given estimates.
Error 9: Service
Self-test discovered circuitry problem, or wrong key pressed during key
test.
Error 10: Insufficient Memory
There is not enough memory available to perform a given operation.
Error 11: Improper Matrix Argument
Inconsistent or improper matrix arguments for a given matrix operation: