Runtime Error 1004 when Copying worksheets from multiple workbooks into current workbook

Hello All! I am attempting to put together a macro that will grab the first sheet of every workbook in a directory, then copy those worksheets into the current workbook one after another. Basically, multiple departments are editing and submitting a workbook. Each workbook has only one sheet in it. I want the macro to open each of those workbooks, copy the only sheet, and insert it into the current workbook one after another. It seems that no matter what I try, I end up getting either a 400 error with no additional information, or (more commonly) a Runtime Error 1004. Here is the code I have so far (cobbled together from various internet sources):

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Thanks in advance!

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should be
and declare variable sourceBook As Workbook

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Thanks for the response! This resolved my issue!!