If it is your top level, you can have these errors when your transistors are NOT connected to bond pads. If they connect to bond pads i would not put tie down cells, it could effect your circuit. For example, if you have an diff amp you have to input transistors vinp, vinm, vdd, vss and output, you would then have two floating gate errors ( or more if your input transistors are fingered or multiples) Then all inputs and outputs go to bond pads, This would then remove your floating gate errors. If you have tie down on your inputs, your amplifier will not work!
When building up in hierarchy you would of course have these dumb floating gate errors, just ignore them! When you are all done and at top level connected to bond pads, then you have to make sure you don't have any errors left!!
Jgk