Thank you for your post.
FileMaker Pro versions 7 through 11 all used the same file format. The file extension is .fp7. Beginning with FileMaker Pro 12, there was a file format change, and the file extension is now .fmp12. FileMaker Pro 12 (and now 13) cannot update FileMaker Pro 11 files directly. Therefore, FileMaker Pro 12 will be unable to see (and access) FileMaker Pro 11 files that are hosted on FileMaker Server 11.
Your options is to update FileMaker Server 11 to FileMaker Server 12/13, or use FileMaker Pro 11 with the files being hosted with FileMaker Server 11.