Arf sorry dude , i forgot to mention that for the moment , your covers must be on your SD card , otherwise if you download some new covers to your HDD , they will get corrupted.....
This is a known issue and R-win will fix it when he comes back from holydays
This happens ONLY with new covers downloaded , or if you create the cache covers (.wfc) from your HDD.
So , move the "boxcovers" and "cache" folders to your SD card , delete the content of the "cache" folder , modify the paths to covers in the wiiflow.ini , and run wiiflow.
At this time , cache covers will be created from your SD , and everything will be fine
And from now you'll be able to download new covers without getting them corrupted.