So there is a limit, but I hit thanks to being upgraded to Office 365 on a new laptop...
The version of Excel that I ran my macros in was set to auto save and it saved my macro file after 5 tabs of data were added so when I ran it the next time it compiled nearly double the data.
I removed the extra 5 tabs of data and was able to import/merge my data as usual. Problem solved.
For reference, the file contains 3,600,917 cells of data and the file is 76,728 KB and it imports just fine. The file with duplicate data contains 6,379,655 cells of data and the file is 124,958 KB and does not import.
The limit is somewhere in between.
------------------------------
Adam Keever
------------------------------