altough this post is from 2013, we encountered this problem too, yesterday (2017) ;)
our root CA is sha512 and 4096bits. the switch refuses to import the root ca cert.
we then installed a lab CA with sha1 and 2048bits root cert. this cert imports fine.
seems like the hp firmware doesn't like the stronger encryption. in 2013... ok.... but in 2017 ?? come on.
model: HPE 1910-8G Switch JG348A
firmware: 5.20 Release 1519P01