IF(AND) function

I have written a very long IF(AND function. Up to 16
nested IF(AND functions. The logic still works and
provides a correct answer. But when I select the cell and
look at the function different characters appear in place
of commas (e.g. a chinese language symbol). Also the
function looks incomplete. If I attempt to click and edit
the cell, excel freezes.

What has happened and what can I do to correct this?