without the full code it's hard to say, and in general uploading screenshots of your code is not very helpful.
Still, the problem is most likely because you're trying to index that array (what ever it is) with a character:
x = 1:10;
x('4');
Index exceeds matrix dimensions.
to understand the root of this error, you need to understand indexing and type conversions
what you did is to index the array with the character 4 which is converted to a number before indexing:
i = double('4')
i =
52
I guess that the array you are trying to index has less than 52 items, and thats were the error comes from
