Changing Admin Page Content

For a plugin I have created an admin menu. Inside this menu I am creating a series of links like so:

<li><a href="<?= $_SERVER["REQUEST_URI"].'?c='.$oClient->Client_ID; ?>"><?= $oClient->FirstName." ".$oClient->LastName; ?></a></li>

Later I use:

if ($_GET["c"]) {...stuff to happen...}

But when I click on the links, I just get a permission error. Any thoughts on why that is happening?