Cause: Tables or table cells that have effects, such as shadows and reflections, can be viewed but not edited in versions of PowerPoint that are earlier than PowerPoint 2008.
Solution: Only use PowerPoint 2008 or later to insert and edit a table.
Some effects and formatting that you can apply to tables or table cells can't be edited when you open the presentation in PowerPoint 2004 or earlier because the effects and formatting are not fully supported in those versions. However, you can still view the table with the formatting or effects because it is converted to a picture when the presentation is opened in PowerPoint 2004 or earlier.
If you apply formatting to the picture while viewing the presentation in PowerPoint 2004 or earlier, then the picture will not revert back to an editable table in versions later than PowerPoint 2008.
Find tables that are not compatible with earlier versions of PowerPoint
Before you save a presentation and send it to someone else, it is a good idea to check for any compatibility issues.
On the View menu, under Toolbox, click Compatibility Report.
Click Check Document.
In the Results list box, click a result.
PowerPoint selects the corresponding, incompatible item in the presentation.