Hi, I removed the Seed_Arduino_FS-1.x.x folder from the libraries folder. I then went to the link from the Wiki to load the SD libraries, and chose the original 1.0.0 release. This seems to work better with the WiFi libraries. As I am new to this platform, I have used very small sketches to try to isolate issues.
I would try writing a sketch that includes the libraries, and then accesses a file, close it, and then access the second file. Once you have that working , you can integrate it into your larger project. I hope this helps, blane