@Gadro without seeing your workflow, it'd be a bit difficult to figure out where in the process the error lies. Any chance you can provide a sample workflow? A few suggestions below:
You may have NaN values in which one or more of your string/categorical fields contain null values (possibly from force changing the datatypes using the select tool). You could use a formula tool to replace these, and then use the ML tool to one-hot encode the categorical variables.
Also ensure that the columns in your dataset contains values that are consistent with the datatype that you've set. For example, Column1 is suppose to contain numeric values but was read in as a string because it contained alphanumeric characters and you force changed the datatype to a float or double. Even though you force changed it, you may still need to clean up the data so that there are no alpha characters.
Hope those suggestions help!