I did a factory reset on the router, and I still got the same error.
all files exists but when I try to use the Luasec module, the error appears.
using opkg I found out that the latest firmware (00.01.11.1) is using luasec 0.8 but the previous firmwareversion (00.01.10) is still using luasec 0.6.
The strange this is that the md5sum of the files in both packages are exactly the same, which means that the library isn't updated from a code point of view.
I think, see first post, that the problem is related to the update of libssl (openssl library)