Permission Denied for SqlDataDictionary

I am trying to truncate one of our tables in a class to run as a batch job, but keep getting a "Request for permission of type SqlDataDictionaryPermission failed. This is on an AX 4.0 system. I followed MSDN example on acquiring permissions and I am an admin. Here's the code:

   //Truncate table

   new SqlDataDictionaryPermission(

               methodstr(SqlDataDictionary, tableTruncate)).assert();

   sqlDict = new SqlDataDictionary();

   sqlDict.tableTruncate(tableNum(PMF_INVENTTABLEMODULELOG),false);

   CodeAccessPermission::revertAssert();

As I stated, I have admin access to this, so should have the required security key. Though this is displaying the (usr) environment in the class list.

Any help appreciated.