Converting nvarchar to int

In SQL 2005 whenever i try to convert an nvarchar to int i received an error that it is not possible. The column with the value looks like this 00000010 and a snippet of the script use to convert looks like this. CAST(substring(UserID,5,3) As Integer)

The table that holds the UserID store the value as a nvarchar. now we are trying to CAST the return substring value to int into another table with the column in new table has int.

much Thanks.