[Q] Getting remote: not allowed when flashing splash image thru fastboot

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I am trying to flash a new splash screen to my rooted T-Mobile mytouch 3g slide thru fastboot and getting "remote: not allowed", my bootloader shows following information:

ESPRESSO PVT SHIP S-OFF
HBOOT-1.02.0000
MICROP-620
TOUCH PANEL-SYNT0104
RADIO-7.15.35.16
Nov 26 2010, 20:43:01

I am currently on latest CM-7 nightly 128 and have been regularly applying nightlies, i had applied OTA Froyo 2.2.1 by HTC sometime back but was able to re-root again thru one-click method.

What could be the problem, is there something wrong with my HBOOT? I had also flashed mtd0.img provided in espresso-eng.zip at Cyanogenmod's wiki for this device and it was successful, but still getting the same error.

Any help please is appreciated.