Hi,
Our jQuery library would be update in the next version of HikaShop in order to not redefine jQuery if already included.
But there is no conflict beween jquery and jquery-ui files.
Please clean your cache after the activation of jquery-easy plugin.
Some page could be still cached and the error would be stored in the cache.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.