Hmm, that sound all a bit weird and I'm afraid you might have to repeat your test and record precisely the error messages you are observing.
I've re-done your test somewhat by booting a "plain" TC 2.11 system (without any persistence, i.e. "cloud" mode) and installed 'conky.tcz' (via command tce-load -wi conky). Starting and running 'conky' went without a hitch, so I'm surprised about your problem. Furthermore I'm surprised about the error you reported since I get the following result:
tc@box:~$ ldd `which conky` | grep libiw
libiw.so.29 => /usr/local/lib/libiw.so.29 (0xb7f06000)
That means that the 'libiw.so.29' library required by 'conky' could be found as '/usr/local/lib/libiw.so.29'
Generally speaking it would be a good idea to use the CLI to download and install extensions, since you could then post the entire response here. Doing this would give us a better chance in troubleshooting your issue. I suspect that something is not working correctly with regards to your USB pen drive, but we would need to know the details of your setup.
Am I correct to assume that you have tried to load via the 'appbrowser' a locally available extension? For this the respective CLI command would be: tce-load -i "$(cat /opt/.tce_dir)/optional/conky.tcz". To receive further help you might want to supply us more details including the setup of your pen drive.