When I want to export the collection having Missing REST Method Error

I have 3 api definitions, under them there are some api requests that i used in test steps, after making some changes on this api definitions when i want to export the collection, it give me "Missing Rest Method" error, the collection is working by it self only when i want to export i am having this error and it tries to me to select a new REST resource to place Request "Rest Request" in from drop down and even i choose one of them the warning poping up again an again and having export with problems,can you help me, how can i fix this problem?