calling dll function

 

Can anybody help.How to call a dll file. i am using this code it is working in visual basic.net. but it is not working in visual basic  please help

 

 Private Declare Function T_prob Lib "C:TProb.dll" (ByVal lfX As Double, ByVal iDf As Integer) As Double
  
 

Private Sub Command1_Click()
 MsgBox (T_prob(0.9, 5))

End Sub

the problem coming is bad Dll calling convention run time error "49"