Cascading down down lists

I have created a spreadsheet with a set of three cascading drop down lists vased on the approach outined in http://www.contextures.com/xlDataVal02.html

I have the following

1. Concept Area (List 1)
2. Subject area within each concept area (List 2)
3. Entity within each subject area (List 3)

Issue I have is I have VB on the worksheet to handle when a drop down is reset, it clears the next dependant drop down (here is the code)

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However if I reset the value in list 1 I need it to clear list 2 and 3, the above code only clears list 2, not 2 and 3. My workaround was to add an if statement to list 3 data validation source (e.g. =if(B2="","",remainingcode). The problem is this approach seems to cause the whole spreadsheet to freeze and go into a loop when I reset values.

Here is a link to the spreadsheet, would appreciate any assistance in resolving this. The tab that has the drop downs is called "CascadeSelect", the data supporting the drop down (i.e. named ranges) are in Sheet2

Thanks - I added the code below to the sheet in VB Editor but it doesn't appear to be doing anything, when I change a list value in list 1 or 2 the cells to the right just stay the same, I just wondered whether i have put the code in the correct pleace? If so, not sure why the code doesn't appear to be doing anything

Thanks so much for your helps so far

Troy