The subnet object '%1' appears in the Configuration\Sites\Subnets container in the DS. The name is not syntactically valid. ...

The subnet object '%1' appears in the Configuration\Sites\Subnets
container in the DS.  The name is not syntactically valid.  The valid
syntax is xx.xx.xx.xx/yy where xx.xx.xx.xx is a valid IP subnet number
and yy is the number of bits in the subnet mask.

Correct the name of the subnet object.