VBA that works perfectly in one file errors out in a new file based off the original!

Morning folks.

I've got a curious one that has been doing my box in for a few hours now.

I have some code in an engineering spreadsheet that selects element types from a combobox, and uses the result of that to update the Validation range in another combobox to allow selection of a particular size of element. This - thankfully - is working absolutely perfectly. See below for the original:

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What isn't working for some ungodly reason is the following code, which is merely a cut-down version of the first, with the initial 'IF' statement removed, as there is only the one combobox set to select from:

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The error appears to be in the Range("mrgChordSectionSize").Value = "", which throws up the "Method 'Value' of object 'Range' has failed" error causing Excel to totally crap out.

Literally all i've done to get from the original (working) file to the new (crashing) file is do a 'Save As...' and delete the 'IF' statement for simplicity, and all hell has broken loose.

Anyone got any ideas what I might be able to try?

Never mind - I've solved it. I obviously had a moment of being stupid, because I suddenly realised that by deleting the 'IF' statement, I accidentally removed the section of code that prevents the Sub being called on every cell change rather than just the target cell change, and thus getting a cascading loop from subsequent changes.

D'oh