Error Handling and linking VBA to specific workbook

Hello everyone. Thank you again for all of your help on my previous thread:
http://www.excelforum.com/excel-prog...on-update.html

Here is the followup / Next steps that I will be working on.

Here was the code I am currently working with:

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My questions are two fold, as mentioned in the title:

Foremost, it was recommended on the other thread that I should include an error handling routine while I work on the code for instances where things simply don't work as intended. I have created a separate sub with Application.enableEvents = True, but was the error handling routine that was recommended I place into the sheet more automated than running a separate macro?

Secondly, this VBA works well, however, I'm having problems if I have two worksheets open. Is there a way to bind this VBA to the single workbook, rather than all excel workbooks open in the Excel instance?

And again, thank you everyone for your help on this project of mine. I'm sure there will be many more questions to follow as I continue to work on this.