For one, you can’t call template files directly as you’re doing… If you want the page somepage, you should call it directly, with the query string arguments added after a trailing slash.
Look into the function add_query_arg() – its a much more bulletproof way of tacking GET variables onto the end of WordPress urls. For example, if you need to call www.example.com/somepage with the query string ?variable=whatever, try calling
add_query_arg( 'variable', 'whatever', 'http://www.example.com/somepage' )
to get the proper url to use. This guarantees getting the proper url in a format that won’t clash with your rewrite rules.