ErrorCheck Question

I'm trudging along, learning VB as I go, and am designing a sample program as I read through a VB manual.

My program is basically a "calculator" for computing response rates, gross sales, overhead costs, etc., for Direct Marketing people.

I have placed an ErrorCheck within a Module to be called from the form.

'Error-Checking
    If ErrorCheck() = 1 Then
    Exit Sub
    End If

In the module I have written:

Public Function ErrorCheck() As Integer

Dim IntPress As Single

'Error-checking for Gross Sales.
If Val(frmQuick.txtPrice.Text) <= 0 Then
    IntPress = MsgBox("Enter a value for the price", vbExclamation, "Gross Sales")
    frmQuick.txtPrice.SetFocus
    ErrorCheck = 1
    Exit Function
End If
If Val(frmQuick.txtSold.Text) <= 0 Then
    IntPress = MsgBox("Enter number of units sold", vbExclamation, "Gross Sales")
    frmQuick.txtSold.SetFocus
    ErrorCheck = 1
    Exit Function
End If
'No error occurred if execution gets here
ErrorCheck = 0
End Function

When the field is blank, the MsgBox and set focus works fine. When the field begins with an alpha character (in case of an inadvertent entry error), then a number, it works fine.

But when I enter a numeral followed by an alpha character I recieve a Runtime Error '13', Type Mismatch.

Where have I missed this??? Obviously some code checking for Alpha Characters???

Thanks for any assistance!