DBNULL Error - SQL Server2000/ASP.NET

Dear Group

I'm having a very weird problem. Any hints are greatly appreciated.

I'm returning two values from a MS SQL Server 2000 stored procedure to my
ASP.NET Webapplication and store them in sessions.
Like This:

prm4 = cmd1.CreateParameter
With prm4
..ParameterName = "@.Sec_ProgUser_Gen"
..SqlDbType = SqlDbType.VarChar
..Size = 10
..Direction = ParameterDirection.Output
End With

prm5 = cmd1.CreateParameter
With prm5
..ParameterName = "@.Sec_ProgUser_Key"
..SqlDbType = SqlDbType.VarChar
..Size = 10
..Direction = ParameterDirection.Output
End With
...
cmd1.ExecuteNonQuery()
...
Session("Sec_ProgUser_Gen") = prm4.Value
Session("Sec_ProgUser_Key") = prm5.Value

Both output parameters are declared as varchar(10) within the stored
procedure. If I run the stored procedure in SQL Analyzer, I'm getting a
string value for each of them. E.g. @.Sec_ProgUser_Gen is "1110011",
@.Sec_ProgUser_Key = "1100".

Now the strange thing happens if I try to run the following code:

Sub MyTest()
Dim MyString1 As String
Dim MyString2 As String
MyString1 = CStr(Session("Sec_ProgUser_Key"))
...
MyString2 = CStr(Session("Sec_ProgUser_Gen"))
End Sub

It fails in line 'MyString2 = CStr(Session("Sec_ProgUser_Gen"))' with Cast
from type 'DBNull' to type 'String' is not valid.

I don't understand this. They are both the same, the only difference is the
length of the string. Help!

Additional Information:
The values for @.Sec_ProgUser_XXX are created in the stored procedure with a
statement like this:
SET @.Sec_ProgUser_Key = (SELECT Convert(varchar(1),Key_CanCreateKey) +
Convert(varchar(1),Key_CanCreateTransaction) +
Convert(varchar(1),Key_CanView) + Convert(varchar(1),Key_CanDelete) FROM
i2b_proguser_securityprofile WHERE SecurityProfileID = @.SecurityProfileID)

The datatype of the source columns used to be bit then changed them to
Integer as I thought this might cause the problem. (Although it shouldn't as
the values get converted to varchar without a problem in the stored
procedure. No fields contain NULL values, only 1 or 0.Hi Everyone

Found the problem. Strange that I haven't seen it earlier.
Dim str1 As String = "EXEC sp_ValidatePermissions @.ProgClientID,
@.ProgUserID, @.Sec_ProgClient_Mod OUTPUT, @.Sec_ProgUser_Gen OUTPUT,
@.Sec_ProgUser_Key OUTPUT"

Forgot OUTPUT for @.Sec_ProgUser_Gen

"Martin Feuersteiner" <theintrepidfox@.hotmail.com> wrote in message
news:bup5nf$5dl$1@.titan.btinternet.com...
> Dear Group
> I'm having a very weird problem. Any hints are greatly appreciated.
> I'm returning two values from a MS SQL Server 2000 stored procedure to my
> ASP.NET Webapplication and store them in sessions.
> Like This:
> prm4 = cmd1.CreateParameter
> With prm4
> .ParameterName = "@.Sec_ProgUser_Gen"
> .SqlDbType = SqlDbType.VarChar
> .Size = 10
> .Direction = ParameterDirection.Output
> End With
> prm5 = cmd1.CreateParameter
> With prm5
> .ParameterName = "@.Sec_ProgUser_Key"
> .SqlDbType = SqlDbType.VarChar
> .Size = 10
> .Direction = ParameterDirection.Output
> End With
> ...
> cmd1.ExecuteNonQuery()
> ...
> Session("Sec_ProgUser_Gen") = prm4.Value
> Session("Sec_ProgUser_Key") = prm5.Value
> Both output parameters are declared as varchar(10) within the stored
> procedure. If I run the stored procedure in SQL Analyzer, I'm getting a
> string value for each of them. E.g. @.Sec_ProgUser_Gen is "1110011",
> @.Sec_ProgUser_Key = "1100".
> Now the strange thing happens if I try to run the following code:
> Sub MyTest()
> Dim MyString1 As String
> Dim MyString2 As String
> MyString1 = CStr(Session("Sec_ProgUser_Key"))
> ...
> MyString2 = CStr(Session("Sec_ProgUser_Gen"))
> End Sub
> It fails in line 'MyString2 = CStr(Session("Sec_ProgUser_Gen"))' with Cast
> from type 'DBNull' to type 'String' is not valid.
> I don't understand this. They are both the same, the only difference is
the
> length of the string. Help!
> Additional Information:
> The values for @.Sec_ProgUser_XXX are created in the stored procedure with
a
> statement like this:
> SET @.Sec_ProgUser_Key = (SELECT Convert(varchar(1),Key_CanCreateKey) +
> Convert(varchar(1),Key_CanCreateTransaction) +
> Convert(varchar(1),Key_CanView) + Convert(varchar(1),Key_CanDelete) FROM
> i2b_proguser_securityprofile WHERE SecurityProfileID = @.SecurityProfileID)
> The datatype of the source columns used to be bit then changed them to
> Integer as I thought this might cause the problem. (Although it shouldn't
as
> the values get converted to varchar without a problem in the stored
> procedure. No fields contain NULL values, only 1 or 0.