The problem is most likely in one of the remotes. Either one has a weak battery or one is failing. If one of the remotes is new then the problem could also be that it is the wrong one for your opener. It could also be that the memory on your opener is full and needs to be erased.
The links below deal with other models but the information and tests will work for your model as well and should help you locate the problem.
If not, or if you have other concerns, feel free to submit another question and we will do our best to help further.