Hp Color laser jet 5550 Having "RFU LOAD ERROR RESEND RFU OVER PARALLEL PORT"

RFU is Remote Firmware Upgrade

.You can send firmware file using parallel cable (using copy /b fw.rfu lpt1: ) only if printer displays SEND RFU NOW (or similar).

Try resetting NVRAM, 

CAUTION: Initializing NVRAM resets the serial number, the event log, the page counts, the calibration settings, and the EIO card. Use the SERVICE menu to restore the serial number and page counts. You also need to reconfigure any computers that print to this product to recognize the product. Initialize NVRAM only when absolutely necessary. In most situations, use cold reset to reset product variables but still retain the needed values in the SERVICE menu.  Before initializing NVRAM, print a configuration page and a supplies status page to gather the following information:
 ● Total page count
 ● Serial number

To initialize NVRAM
1 Turn the printer on and watch the control panel display.
2 When the display begins showing the memory count, press and hold (down key) until all three lights on
the control panel are lit.
3 Press (up key) .
4 Press PAUSE/RESUME. The display should show SKIP DISK LOAD.
5 Press (up key) until NVRAM INIT is highlighted.
6 Press OK. The printer will initialize NVRAM and then continue its power-on sequence

if this doesn't help, Don't thing any Change the Firmware DIMM. It wil be fixed.