I'm sure Microsoft has invented new and wackier ways of doing everything in later versions of Excel, but in my Excel 2003 you can change macro security levels under menu item Tools - Macro - Security. My security level is normally set to Medium, which warns that a spreadsheet contains macros when you try to open it, but allows you to go ahead if you say Yes.

One other note: I adapted this from an earlier spreadsheet I used for converting between GPX and KML formats for my GPS, and I guess it still has some invisible "Data Validation" rules embedded in the Excel sheet.

This is how to get rid of them:

- Select the entire sheet (click the upper left header cell as a shortcut)
- Select from the Excel main menu Data - Validation.
- It will tell you that there is more than one type of Validation in the selected cells and offer to clear the validation rules from all of them. Say Ok, and then apply the default validation rule "Any value" to all cells.