MS Excel: HEX2DEC() does not work with cell references?

How can you convert a column of hex numbers to a new column of decimal numbers? If I have a hex number, say "1F24A0" in cell C2, and in cell D2 I put the formula "=HEX2DEC(C2)" it does not work (just results in "#NUM!"). It does work with a hex literal, like "=HEX2DEC("1F24A0") but I need it with a cell reference. I am using Microsoft Excel 2007 on WinXP.