|The memory card has failed or just worn out and will have to be replaced.|
Buy a good quality brand like Lexar, Sandisk or Kingston as some other brands are not as reliable.
When on vacation or indeed anywhere away from home, you really need to have some means of copying the card contents to another location as a backup. I always take my laptop & card reader with me and copy card contents to my laptop every time there are any new pics on it, just in case the card decides to pack up.
If taking a laptop is not possible, many people take one of these or something similar with them: http://www.bhphotovideo.com/c/produ...