i am newbew

i am trying to install roundcube on ubuntu 16.10 that is on Virtual Machine

my host computer - windows 7 32 bit

guest computer - ubuntu server 16.10 32 bit

roundcube ver - 1.2.3 complete

getting error on -  webmail/installer/index.php?_step=3

error is - IMAP errror 

sir help me out in this error

thanks and regards in advance