Hey there @dpsh! Do you happen to have RStudio installed? I ask, because I noticed this little tidbit:
The version of DADA2 deployed with QIIME 2 2018.2 is version 1.6.0, not 1.4.0. We usually see this kind of version mismatch whenever RStudio is around. If that is the case, check out this post for suggestions on how to fix:
https://forum.qiime2.org/t/rprofile-and-libpaths-with-dada2-exit-code-11/1519/5
Let us know how it goes, and if you're still stuck we can come up with some additional ideas!
Thanks! 