Column not added; It is the wrong type for list

[#1]

I am getting the above error when i am trying to add 2 columns for the bubble plot. I am not abl to change it to continuous as it is greyed out but only between ordinal and nominal. 

[#2]

I appears that you have defined the columns as character columns.  Character columns can not be continuous.

[#3]

You can often change the variable type (even when it is greyed out) by going to Column Information and changing it there.  Of course, to change from nominal to continuous, you will want it to be numeric data - this is just a work around when the drop down in front of the variable is greyed out.