Going to need more info, your system, anything else installed and how you iunstalled nextcloud and from where?
I do have it installed and running on a sme10 RC1 never saw that error.
Having said that Nextcoud is yet to be released to contribs for sme10, it is still in /smetest and /smedev places you take your chances with and can expect things to break, remeber the wiki is for sme9, eg it details fws repo as part of install, sme10 does not use it.
Anything installed from /smetest is a watch and see, and /smedev is danger will robinsonb time
Good Luck