I found that the following instructions from here worked for me on Lubuntu 15.10
Unprotected network folder won't automount
I've had a situation where an unprotected network folder wouldn't automount during bootup, but after manually entering "sudo mount -a" was mounted correctly. I solved this by replacing the "guest" option by "username=guest,password=".
//servername/sharename /media/windowsshare smbfs username=guest,password=,uid=1000,iocharset=utf8,codepage=unicode,unicode 0 0
Mount password protected network folders
The quickest way to auto-mounting a password-protected share is to edit /etc/fstab (with root privileges), to add this line:
//servername/sharename /media/windowsshare cifs username=msusername,password=mspassword,iocharset=utf8,sec=ntlm 0 0
Additional to this I used the following option to assure auto mount works:
_netdev
//servername/sharename /media/cloud cifs _netdev,uid=1000,gid=1000,dir_mode=0700,file_mode=0600,nounix,forceuid,forcegid,credentials=/home/myuser/.smbcredentials,iocharset=utf8,sec=ntlm 0 0