It sounds like you moved the ExcelImportOverview page from it's original module to MyFirstModule. If that was by mistake, you can move it back to the Excel Importer module. If not, open the page and open the "allowed roles" or "visible for" option and choose the module roles that you want to have access to the page.
Sometimes you need to untick any already ticked option and re-tick it again. If you don't, Mendix will keep mentioning the error. As Eric mentioned, this usually happens when you move stuff around.
I had the same problem after moving 5 microflows (on purpose) to another module, untick-retick the appropriate role did not solve the problem, moving them back to the original module didn't solve the problem …. hmmm
My solution was to duplicate and move to the intended module, after that I had to fix the buttons who called those microflows and delete the errorous ones.
Hope this helps,
I found this forumpost to solve my problem: edit via the properties window: https://forum.mendix.com/link/questions/9420
thank you Thijs Schoenmaker.