I cant believe I have never come across this problem before (Its now about 14 years working with VB6 on a daily basis)

I tested software on my machine - worked well !
Ran on the customer machine and kept getting strange results

Finally tracked it to this statement

ValIncTax = Val(txtInvValue.text)

ValIncTax is a Currency Type
txtInvValue.text is a Text Box
Here is the problem

The Text Box had the value formatted as ##,###,##0.00
eg, 3,245.65

What was being transferred to ValIncTax was just the 3 ! (The rest was truncated off)
Worked on my machine because I was using figures no larger than 999.99

So there's one for the books !