Database implementation: having trouble with castException for this function

I keep getting either a Infinite loop error or a invalidCastException for this function not sure why.
I am looking to create a function that can be used in Click events to change the color of the background.

Code:

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Function BackEndColors(ByVal strTheme As String)
        ''Checks to see if user selected ThemeColor''
        ''CStr converts data table row 0 , item 0 to a string - inline for better performance
        strTheme = CStr(dtThemeColor.Rows(0).Item(0))

        If Not (strTheme <> Nothing) Then
            ''if the user has a preference set in their user account information

            ''nested If''
            ''makes color of background fit users preference''
            If strTheme = "Default" Then
                pnlTitle.BackColor = Color.SteelBlue
                Me.BackColor = Color.FromArgb(122, 154, 186)
                lilRegister.LinkColor = Color.LightSteelBlue

            ElseIf strTheme = "Green" Then
                pnlTitle.BackColor = Color.DarkOliveGreen
                Me.BackColor = Color.OliveDrab
                lilRegister.LinkColor = Color.Navy

            ElseIf strTheme = "Blue" Then
                pnlTitle.BackColor = Color.MidnightBlue
                Me.BackColor = Color.DarkSlateBlue
                lilRegister.LinkColor = Color.PowderBlue

            ElseIf strTheme = "LightBlue" Then
                pnlTitle.BackColor = Color.FromArgb(0, 105, 183)
                Me.BackColor = Color.FromArgb(69, 132, 207)
                lilRegister.LinkColor = Color.Navy

            End If
        Else ''If user didn't select color''
            ''Default Theme''
            BackEndColors("default")

            ''Default ThemeColor''
            strTheme = ""
        End If

        ''null pointer - Void Function''
        ''needed for NullPointerException''
        Return Nothing

    End Function

---

Where are you getting the error?

You have this defined as a function but you have not defined the type the function is to return and the only code I see that returns something actually returns Nothing which makes no sense at all.

You also have the function set to take a parameter but then you do nothing with that parameter.

You call the function again in your else case and since the condition that caused the else to trigger has not changed then it will fall into an infinite recursion until it hangs or crashes.

Overall the design is very poor and needs to be re-written

InvalidCastException usually refers to a conversion that cannot be made. So somewhere in either your DB or your function you have incompatible types, or trying to convert something into a wrong type. It can also mean that you may have a NULL value in your table