When did this start happening? Have you moved any receivers or equipment? How many receivers do you have? Is this happening on more than one receiver? Is the green light lit on the power inserter? Have you unplugged the power inserter until the green light goes out, then plug it back in?
A 775 error code means your receiver/dvr isn't communicating with the dish. If you have a power inserter, check to be sure that it's plugged in and working (green light on). Also check all of your connections to be sure they are tight.