This really a spelling issue:
(defun get_line_by_start_or_endpoint ( x tol /)
(ssget "X" (list '(-4 . "<OR")
'(-4 . "<AND")
'(-4 . "<=,*,*") (list 10 (+ x tol) 0.0 0.0)
'(-4 . ">=,*,*") (list 10 (- x tol) 0.0 0.0)
'(-4 . "AND>")
'(-4 . "<AND")
'(-4 . "<=,*,*") (list 11 (+ x tol) 0.0 0.0)
'(-4 . ">=,*,*") (list 11 (- x tol) 0.0 0.0)
'(-4 . "AND>")
'(-4 . "OR>")
'(0 . "LINE")
'(8 . "0")
)
)
)
BTW: You should not use the 'C:' prefix for this type of function.