@sangasangasanga If u want all text after 68 indexNo. Use Below condition
If u want certain number of number letters from 68 indexNo. Use Below condition
where number is number of characters u required from 68 position
What happening in ur case is
Ex. ur variable contains 80 letters, ur give starting index as 68, variable.length gives u 80.
From 68 it cant copy 80 characters, since total length of string is 80 itself. So give number of characters u required in that place, otherwise remove that field.