Excel 2010 :: Replicate Conditional Formatting Using A User VBA Function?

Using Excel 2010.

The background to this question is that I'm trying to replicate conditional formatting using a user VBA function, because I require a thick border around the cells (and the conditional formatting within Excel only has thin borders)

In the final function, there will be 9 combinations of formatting {Red, Amber, Green} interior with {Red, Amber, Green} thick borders.

The formatting is determined by a number in another cell (the "target" cell), which returns a value 0,...,8

I've only got as far as filling in the interior for the first combination, but the function returns an error "Application-defined or object-defined error".

VB:
Function VBA000_003_SetRAG(strTargetRange As String) 'strTargetRange is the reference for the target cell that contains the value 0,...,8

On Error Goto handler [code]....

There is not a problem with the target range, if I remove the two lines relating to rngCaller then the function works OKExecuting the rngCaller.Interior.Color = RGB(255, 0, 0) command through the Immediates window works OKI've tried calling a subroutine & passing the range across

Same errorChanging the range in the subroutine to an absolute range (eg. Sheet1.range("A1")) also causes the

same errorExecuting the subroutine on its own (with the absolute range) works OK

So my guess is that it's a bug/limitation with Excel VBA when trying to execute commands from inside a user function