Question: When I am trying to open password-protected ppt with libre office 3.5 in Ubuntu 12.04,it gives me a message says "Read-Error. loading of password-encrypted microsoft powerpoint is not supported."So is there any solution to this?

Answer: 
Open it with powerpoint and save it without password encryption...
The ppt you are trying to open in Libre is password protected in MS office. Libre Office cannot open such password protected files. So, for this, Install **Wine Windows Program Loader** software from Ubuntu software center and then open yout .ppt with it.