How to use a remote $_POST

In my module I receive a value from another application via a $_POST['testvalue'] that redirects to a drupal site.
This is allocated to a variable $somevalue=$_POST['testvalue']
I can then display this value using print_r or whatever.
The problem is that i want to save this information into a database with the piece of code below but for some reason i cant.

$somevalue=$_POST['testvalue'];
db_query("INSERT INTO {datasubscriber} (subscriber) VALUES ('%s')", $somevalue);

Anybody any ideas?