WordPress editing meta_value does not work after update

I have problem while editing meta_value.

What I did: I edited meta_value. After edit, I do not get value. What could be problem?

I think does it counts character. How can I fix it? Please guide.

For Eg:

a:1:{s:13:"administrator";b:1;}

when i edit this field from database and change to

a:1:{s:13:"administratortypea";b:1;}

i wp_meta() returns blank value