Saving macros and deleting macros from a macro file creates holes in the macro file structure or causes it to become fragmented. The Pack command compresses the file and fills in the holes created by the changes to the file. This is similar to performing a defrag on a hard drive, only it will take less time.
You may see this warning as you begin the Pack process. Since Macro Express uses index numbers to track each macro in the file, packing may reorder the index numbers. This may cause the macros in the popup or floating menus to be reordered.
Macro Express - Explorer > Tools > Pack