Why is the Data Validation icon in the Data part of the Excel 2010 Ribbon disabled?

Dear colleagues,

I am using Excel 2010.
I exported information from Microsoft Dynamics CRM for enrichment to an XML file, with the intention to apply Data Validation on one of the columns.
When I opened the XML file I realized the Data Validation icon in the Data part of the Excel 2010 Ribbon was disabled.
I then saved the file as .xlsx, hoping that icon won't be disabled, but it still is.
It is a stand alone file without any sharing or other complexities (other than the fact it had originated from that XML file).
Why is the Data Validation icon in the Data part of the Excel 2010 Ribbon disabled?
How can I enable it, if at all?

Thanks for answering,
Ron.

Attach a sample workbook. Make sure there is just enough data to make it clear what is needed. Include a BEFORE sheet and an AFTER sheet in the workbook if needed to show the process you're trying to complete or automate. Make sure your desired results are demonstrated, mock them up manually if needed. Remember to desensitize the data.

Click on GO ADVANCED and use the paperclip icon to open the upload window.

View Pic

Added the sample Excel file.
Found the solution by myself: there was a lock on the workbook to prevent from unauthorized data changes.

There must be something wrong with the file itself. I copied the data into a new workbook but I can't activate right to left editing....you will have to do that. The Data Validation however is now shown as are the worksheet tabs.