Hi Gary,
Try it in the Designer first, then use the same syntax.
I believe the problem is since you are entering a number you have to convert the number to a string in the formula, even though you declaring in VB they are strings CR see's it as a number, until converted:
Dim cboSKU As String = ComboBox1.Text ' <== the value of the combobox is 1234
Dim myFormula As String
myFormula = "{INVEN.SKU} = ToText(" + cboSKU + ")"
MessageBox.Show(myFormula)
I can't be specific because you did not say what type of field {INVEN.SKU} is.
You may need to convert it ToNumber.
Bottom line is you need to keep your types in order. but test in Designer, if it doesn't work there it won't work in code...
Don