1. what is an LG om7550d?
2. what is D-PROTECTION?
When requesting information it is polite (and good practise) to at least post a link to the equipment, a (potential) user manual/schematic and as much detail as may be required to FULLY EXPLAIN the problems.
Or are we expected to do all the above as well as find a fix for you?
The error message seems to be generic so may need to troubleshoot this in the traditional way, starting with a description of what it isn't doing, when that message appears, and what you have observed inside visually and with a multimeter.