df: a line in /etc/mnttab has too many fields
This issue can arise because of reasons like - wrong formatting of vfstab, auto_master files.
If you want to see if a white space is the problem, you should do a "view /etc/mnttab" and then input ":set list". This will display TABS as "^T" symbols. Spaces will show up as spaces. The issue is with files like /etc/vfstab, /etc/auto_master and such are white space delimited already so looking for spaces in there is going to be somewhat fruitless as a space between fields is perfectly acceptable.
Most of the time
Anything found in /etc/mnttab has already been accepted by the kernel as a valid mount. /etc/mnttab is a kernel created and maintained file.
I was having backup copy of vfstab file I simply replaced it with original and issue disappeared.
This is pretty hot tip!