Cannot create a new worksheet manually or with a macro. ("That command cannot be used...)

I have a recent error that I need to solve quickly but I haven't seen this before. In my .XLSM file when I go to create a new worksheet manually I get the error "That command cannot be used on multiple selections". Does anyone know what Excel is talking about here?

EDIT: When I go to open the file from a fresh start I get the message "Excel found unreadable content in 'file_name'. Do you want to recover the contents of this workbook? If you trust the source of this workbook, click yes.

So I clicked yes and... The message "Removed Feature: Data validation from /xl/worksheets/sheet32.xml part" happens. Has anyone seen this before and how did you fix it? (I will not be able to upload the full workbook.)