The cache isn't at the posted coordinates. To find it you must solve this logic-based puzzle based on the Battleship guessing game. If you enjoy sudoku or paint-by-numbers puzzles (also known as Nonogram, CrossPix, and PictureLogic), you may enjoy this too.
One of my favorite logic-based puzzles is "Battleships", which also goes by Bimaru, Solitaire Battleships. or Battleship Solitaire. Below is an easy one for you to solve. From that, you'll be able to get coordinates to the cache.
This grid represents a section of ocean in which a fleet is hiding. This fleet consists of one battleship (four grid cells in length), two cruisers (three cells each), three destroyers (two cells each) and four submarines (one cell each).
The ships may be oriented either horizontally or vertically, and no two ships can occupy adjacent grid cells, not even diagonally. The digits along the grid's right and bottom edges indicate the number of cells in the corresponding rows and columns that are occupied by vessels.
Notice that three "shots" have already been taken to start you off. They show two grid cells with water (no ships located there) and the end of one ship. See if you can plot the locations of all 10 ships.
Once you've located the fleet, it's time to calculate the coordinates. If a letter is on a ship, use the size of that ship. E.g., if A is on the battleship, then A = 4. If A is in open water, then A = 0.
The solution is:
North [A+B] [B+C] ° [B+E] F . F [B+D] A
West A C C ° [D+C] [G+H] . [C+I] [J+K] [F+J]