Is your Numbers document locked? Or are the Tables in Numbers locked?
To lock or unlock a Table in Numbers, click on the Table in the left pane ('Sheets'). Then:
Pages > Menu > Arrange > Lock or Unlock
If your Numbers document is locked, there is another problem. Please reply with more information.
Thanks for the green tick.
The Number'09 User Guide (download from the Help Menu in Numbers) explains how to password-protect a document (Page 31) and how to lock a document (Page 34).
When you import an Excel document into Numbers, the Excel password protection is removed. You can add password protection to a Numbers document, but that may not carry over if you export to Excel.
You can export from Pages to PDF and lock the PDF file. Page 237 of the Numbers User Guide: Exporting a Spreadsheet in PDF Format
- 5 Click the Security Options disclosure triangle to password-protect the PDF.
Ian.MacBook Pro (13-inch, Mid 2012), OS X Mountain Lion (10.8.3)