' Error [3]: ERROR_INVALID_CMD '

Can anyone explain the cause and solutions of this error?
It appears when I try to Read my logged data from the SD
card using Navilink.

The information menu on Navilink displays this (sorry for the lengthy

'Genie GT31 device found
NVK.EXE -C 15  -R SBPH "E:\GPS_data\BGT31_GPS\Saved_GPS_data\GRE737_833000767_20090220_200338.sbp"
Flash log data header read successfully!... 
NVK.EXE -C 15  -L "E:\GPS_data\BGT31_GPS\Saved_GPS_data\GRE737_833000767_20090220_200338.sb1"
Flash log data downloaded successfully! 
SBP File created.
myappend.bat "E:\GPS_data\BGT31_GPS\Saved_GPS_data\GRE737_833000767_20090220_200338.sb1"  "E:\GPS_data\BGT31_GPS\Saved_GPS_data\GRE737_833000767_20090220_200338.sbp"
NVK.EXE -F SBP "E:\GPS_data\BGT31_GPS\Saved_GPS_data\GRE737_833000767_20090220_200338.sbp"  "E:\GPS_data\BGT31_GPS\Saved_GPS_data\GRE737_833000767_20090220_200338"
Operation failed'

So, it seems that Navilink successfully starts to read data, but for some
reason it fails on the way through... My GPS is flashed with firmware
1218 (as provided from website) and I used NMEA during
logging with all NMEA options set to 1 sec interval.
I've tried to reinstall Navilink, attempted to read data several times
but it still resists to work...



Another window appears when I try to download data from my SD card to PC:

'NAVILINK command line version V1.64(B20080715a) Locosys, 2007'

then I press OK and another error follows:

'Error[5] UNDEF ERROR'

Ok, I think I would better take off SD card from GT31 and stick it to an
external SD card reader... This avoids all kind of problems - I will
continue using Navilink as a file format convertor only.