A "corrupted memory card" prompt means that the SD card is either non-readable or the data therein is corrupted, causing improper device operation. The causes for this are, but are not limited to, the following: errors in data reading and writing, malicious files, user-fault, external damage or factory defects.
The best method of recovering the lost data is to use an SD card recovery utility software, many of which are free and easy to use. Once a user has determined it is corrupted, he should cease use immediately and either purchase or download a free utility, use it to search for the corrupted or missing files, then restore them.
Memory card owners should keep in mind that some programs have a limited range of file types they can recover or can only restore recently deleted data. If users run into such issues, they should try using another utility.