My advice is to look for the values in Frozen that contain whatever it is preventing the column from being interpreted as numeric. In your example data, the values of Frozen are integers. If that is generally true, then
NonNum <- grepl("\\D", Vekt$Frozen)
BadRows <- Vekt[NonNum, ]
will give you a data frame with the rows that have non numeric characters. If there are decimal numbers or scientific notation, the problem is more difficult.