[no such file or directory]

I'm trying to run btsync on my NAS which runs linux on an ARM processor. Here's what I get.

root@fileserver:/mnt/HD_a2/btsync# ls -l

total 6688

-rw-rw-r-- 1 nobody 502 155 May 7 09:16 LICENSE.TXT

-rwxrwxr-x 1 nobody 502 3412684 May 15 08:41 btsync

-rw-r--r-- 1 admin 500 3420160 Jun 21 21:25 btsync_arm.tar

root@fileserver:/mnt/HD_a2/btsync# ./btsync

-sh: ./btsync: No such file or directory

Any thoughts as to why this is? Thanks.