Unable to paste items in MS Powerpoint on a MacBook

[An Gof]

I seem to have suddenly developed a problem with Powerpoint on my Apple MacBook.
When i copy a photo to insert into a presentation the paste function under the Edit menu is greyed out and not available.
This happened without notice part way through working on a presentation. Can anybody help me to solve this issue? I have googled the problem and tried the "pboard" suggested solution to no avail.
Help!!

 

[Sparrow]

Rather than copy & paste, can you just drag the picture in?

 

[JP1]

You haven't locked the PowerPoint have you?

 

[JP1]

Try creating a new tile window and see if you can do it in a new slide. I had that once and just deleted the corrupt slide