The error message is pretty explicit:
Index was out of range. Must be non-negative and less than the size of the collection.Parameter name: index
The value of index is either negative, or invalid. Remember, .NET array indexes start at zero, and go up to the number of elements minus one, so if you have three elements in your array, valid indexes will be 0, 1, and 2 - any other value will give you this exception.
You need to find out what
index
is, and how big the
gv_admin.Rows
collection is. We can't do that - we don;t have any access to your data, or your code while it's running.
So, it's going to be up to you.
Fortunately, you have a tool available to you which will help you find out what is going on: the debugger. How you use it depends on your compiler system, but a quick Google for the name of your IDE and "debugger" should give you the info you need.
Put a breakpoint on the first line in the function, and run your code through the debugger. Then look at your code, and at your data and work out what should happen manually. Then single step each line checking that what you expected to happen is exactly what did. When it isn't, that's when you have a problem, and you can back-track (or run it again and look more closely) to find out why.
Sorry, but we can't do that for you - time for you to learn a new (and very, very useful) skill: debugging!