To replicate this error - do the following :-

 - Choose a cell - and type in the word 'Destination' 
 - Then choose a different cell and type in the word 'Source'
 - Now add a comment to the 'Source' cell.
 - Copy it using CTRL-C
 - then put the focus onto the Destination cell, and use PasteSpecial ( 
selecting only Notes ( ie Comments ) to Paste over the Destination
ERROR OCCURS
 - The cell's contents gets wiped ( whether it is a formula or just text )



There is a Sub issue here with regard to Comments being called Notes on the 
PasteSpecial popup - Perhaps you could address that as well ( unless there is a 
good reason for retaining the word 'Notes' )