General Recipe Trouble Shooting

I followed the chef's recipe very closely.  The polenta turned out delicious.  I then took the leftovers and molded them into a cake pan and refrigerated overnight. 

Tonight for dinner, I attempted to saute them in a steel saute pan and the slice of polenta basically fell apart.  I then tried it again using a non-stick pan and encountered the same result.

Any suggestions as to why the polenta slice came apart while in the saute phase would be greatly appreciated.

Thanks.