The text entered for the value table is not valid. A value table is a table containing one or more columns. Each column corresponds to a value in the parameter being defined. The Union tool, for example, requires the path to a dataset or a layer name, along with a priority rank for each input entry. A value table for Union requires two columns: one for the data and one for the priority rank.
Check that the correct value is specified for each column. For help using value tables in scripting, see Using value tables.