ORA-00936 Missing EXPRESSION error when WHERE clause is used

I have a query ending with a where clause:

WHERE       C.CUSTOMER_ID   IN (@CustomerID)";

My OracleDataAdapter contains this line:

oracleDataAdapter.SelectCommand.Parameters.Add(new OracleParameter("@CustomerID", OracleDbType.NVarchar2)).Value = (string)args["CustomerID"];

CustomerID = 00000081

For filling the DataTable I have...

oracleDataAdapter.Fill(dataTable);

Unfortunately it is also here where it throws the ORA-00936 Missing EXPRESSION error When I remove the where clause it run perfectly.

Any idea what is wrong with my where clause or parameter definition?