well.. newest versions of transmission requires libevent-2.x to be installed on your NAS. Most likely on your NAS is libevent-1.4.x (you can check that with ipkg list_installed | grep libevent).
You can try to update libevent from optware (latest version is available), but in my opinion its risky due to current libevent on your NAS is used for some other system stuff.. if you will upgrade libevent to 2.x something else might conflict and not work… so I dont reccomend it…
You can always try to compile transmission from source or cross-compile it - ive done that before (and in process of writing HOWTO about it, but its taking long time, becouse I do that slowly when i have time and right mood). Of course it requires some knowledge about linux..
