Problem with IAP on LPC2138

The IAP is driving me crazy. When I single step my code using ulink it works, but when I just let it run the micro reboots itself and the IAP hasn't worked. I've read the manual, AN10256, searched the forums and looked at the sample code.

Here's my code:

ErrorCode_t writeBufToOneFlashSector(uint8_t secNum)
{
    BOOL good = TRUE;
    ErrorCode_t retCode = ERR_NO_ERROR;
        unsigned int enables;
    BOOL pllStat;

    // Disable interrupts during erase and write operations
    // Keep a copy of what was enabled
    enables = VICIntEnable;
    command[0] = IAP_PrepareSectors;
    command[1] = (uint32_t)secNum;
    command[2] = (uint32_t)secNum;
    waitTXComplete();
    pauseTX(TRUE);
    pllStat = usePLL(FALSE);
    iap_entry(command, result);
    good = (BOOL)(IAP_CMD_SUCCESS == result[0]);
    if(!good)
    {
        usePLL(pllStat);
        retCode = ERR_IAP_ERASE_PREPARE | ERR_NUM_USED;
        errVal = (ParamType)result[0];
    }
    else
    {
        command[0] = IAP_EraseSectors;
        command[1] = (uint32_t)secNum;
        command[2] = (uint32_t)secNum;
        command[3] = XTAL_OSC_KHZ;
        // Disable interrupts during erase
        VICIntEnable = 0;
        iap_entry(command, result);
        VICIntEnable = enables;
        good = (BOOL)(IAP_CMD_SUCCESS == result[0]);
        if(!good)
        {
            usePLL(pllStat);
            retCode = ERR_IAP_ERASE | ERR_NUM_USED;
            errVal = (ParamType)result[0];
        }
    }

    // See about doing the write
    if(good)
    {
        command[0] = IAP_PrepareSectors;
        command[1] = (uint32_t)secNum;
        command[2] = (uint32_t)secNum;
        iap_entry(command, result);
        good = (BOOL)(IAP_CMD_SUCCESS == result[0]);
        if(!good)
        {
            usePLL(pllStat);
            retCode = ERR_IAP_WRITE_PREPARE | ERR_NUM_USED;
            errVal = (ParamType)result[0];
        }
    }

    // Ready to write at last
    if(good)
    {
        command[0] = IAP_CopyRAMtoFlash;
        command[1] = SectorStartAddr[secNum];
        command[2] = (unsigned int)nvBuf;
        command[3] = FLASH_NV_PAGE_SIZE8;
        command[4] = XTAL_OSC_KHZ;
        // Disable interrupts during erase
        VICIntEnable = 0;
        iap_entry(command, result);
        usePLL(pllStat);
        VICIntEnable = enables;
        good = (BOOL)(IAP_CMD_SUCCESS == result[0]);
        if(!good)
        {
            retCode = ERR_IAP_WRITE | ERR_NUM_USED;
            errVal = (ParamType)result[0];
        }
    }
    pauseTX(FALSE);
    return retCode;
}