Unexpected error using the sum function in a QoQ

While attempting to run the following code

<cfquery name="Lev1CatTotal" dbtype="query">
    SELECT 
        SUM(AMOUNT) AS TOTAL
    FROM 
        ChartData
</cfquery>

This is the error message that's generated:

Query Of Queries runtime error. The aggregate function [SUM(expression)] cannot operate on an operand of type [JAVA_OBJECT]

This code works fine when aggregating smaller amounts. However, these are the amount in the table I'm aggregating. This particular query sums to over $5.7B.

Just to move forward, as a workaround, I recoded this as follows:

<cfset TOTAL = 0>
<cfloop query="ChartData">
    <cfset TOTAL = precisionEvaluate(TOTAL + AMOUNT)>
</cfloop>

Using precisionEvaluate(), it casts the TOTAL to BigDecimal precision and avoids the error. Does someone know of a QoQ solution using the sum() function to cast this to a big decimal and avoid using this workaround? Thanks.

Big thanks to @BernhardDöbler for getting me to look into where ChartData comes from. Since this was inherited code, I had to look into this. It turned out that ChartData was created with the following line of code.

<cfset ChartData = QueryNew("FISCAL_YR, GOV_LEVEL1_CAT, AMOUNT")>

I noticed, the original coder didn't specify any data types for his QueryNew() statement, so I modified the line of code to

<cfset ChartData = QueryNew("FISCAL_YR, GOV_LEVEL1_CAT, AMOUNT", "VarChar, VarChar, Double")>

Once I added the Double data type to the AMOUNT column, it corrected the error when I restored back to the original code of

<cfquery name="Lev1CatTotal" dbtype="query">
    SELECT 
        SUM(AMOUNT) AS TOTAL
    FROM 
        ChartData
</cfquery>

and I was able to remove my workaround code which performed the aggregation using a <cfloop>.