Can I add user and passw to my OLAP ConnectionString?

Hi all,
I have written a custom assembly that works fine in preview mode, but when I deploy the report I get the '#Error' message instead of the output.
I have copied the assembly to the bin folder of Reportserver, placed it in the GAC and even edited the policyfiles.

Any help would be very appriciated,

Thanks in advance

public static class SimCardBuyer
{
public static string ReturnBuyer(string Seller, string PeriodeCode, string ComDevice)
{
string connstring = "PROVIDER=MSOLAP;DATA SOURCE=srv03-gc-10;INITIAL CATALOG=Invoicing";
AdomdConnection conn = new Microsoft.AnalysisServices.AdomdClient.AdomdConnection(connstring);
//Create a new string builder to store the results
System.Text.StringBuilder result = new System.Text.StringBuilder();
//Connect to the local server
using (conn)
{
conn.Open();
//Create a command, using this connection
AdomdCommand cmd = conn.CreateCommand();
cmd.CommandText = @."SELECT NON EMPTY { [Measures].[InvoiceAmount] } ON COLUMNS, NON EMPTY { ([Buyer].[Company].[Company].ALLMEMBERS ) }
DIMENSION PROPERTIES MEMBER_CAPTION, MEMBER_UNIQUE_NAME ON ROWS FROM
( SELECT ( { [Com Device].[Com Device].[" + ComDevice + @."] } ) ON COLUMNS FROM
( SELECT ( { [Invoice].[Period Code].[" + PeriodeCode + @."] } ) ON COLUMNS FROM
( SELECT ( { [Seller].[Company].[" + Seller + @."] } ) ON COLUMNS FROM [Invoicing])))
WHERE ( [Seller].[Company].[" + Seller + @."], [Invoice].[Period Code].[" + PeriodeCode + @."], [Com Device].[Com Device].[" + ComDevice + @."] )";

//Execute the query, returning a cellset
CellSet cs = cmd.ExecuteCellSet();
//Output the column captions from the first axis
//Note that this procedure assumes a single member exists per column.
TupleCollection tuplesOnRows = cs.Axes[1].Set.Tuples;
if (tuplesOnRows.Count > 1)
{
for (int row = 0; row < tuplesOnRows.Count - 1; row++)
{
result.Append(tuplesOnRows[row].Members[0].Caption);
result.Append(" / ");
}
result.Append(tuplesOnRows[tuplesOnRows.Count - 1].Members[0].Caption);
}
else if (tuplesOnRows.Count == 1)
{result.Append(tuplesOnRows[0].Members[0].Caption);}
else{result.Append(Seller);}
conn.Close();
return result.ToString();
}
}

Dear readers,

I have solved the problem above, but now I get an error with the Connectionstring.
I'm getting the next error now:

Either the user, NL01\SRV03-GC-10$, does not have access to the Invoicing database, or the database does not exist.
NL01\SRV03-GC-10$ is not a user in my system, so I'm stunned with this strange error.

I would appriciate any reply on this.

regards.