Could this because there are non-numeric values in the column TextValue?
I found 2 null values and entries with multiple minus signs '----' and decimal points '.....' and '-00000' and removed those records.
The form in this case prevent the user from entering any non-numeric characters.
NOTE:Other forms allow alpha characters into the same column with different ParameterID values, that is why the column is not declared as a numeric type.
SELECT * FROM ParameterEntries
WHERE ParameterID = 239
ORDER BY TextValue
Returns > 127,000 records, so it is difficult to tell if any non-numeric characters are mixed in, but the 1st char appears to be numeric by scrolling through all start with 0-9.