Cryatal Report Error: Failed to open the report in the ras server: Class not registered

my senioro wise Crystall report HTML privew is not working can any one please help me when im clicking its asking BOE Server setting.

i googled it but i didnt find any links related that 

while im opening html preview like this error msg coming

"Failed to open the report in the ras server: Class not registered - HTTP commuicationAdapter"