Typing a comma or a dollar sign in a numeric entry in a spreadsheet cell will cause Claris Resolve or ClarisWorks to see the entry as text, rather than as a number. In other words, if you type '12,000' into a cell formatted as currency, the entry will show up without the dollar sign, and will be aligned left. If you then try use that cell in the formula of another cell, the entry in that cell will be seen as zero.
To solve the problem, remove any non-numeric characters from the cell.