CCTK v4.1.0 --ValSetupPwd not accepting BIOS Admin password

Hi,

I'm trying to use CCTK to change the BIOS Admin password on a Precision M3800, using the command:

C:\>cctk --ValSetupPwd=obfuscated --SetupPwd=newpassword
The setup password provided is incorrect. Please try again.

The password *is* correct; I've restarted the system several times to enter the Setup and check that it's still valid!
If it makes any difference to the advice given, the current password is all lowercase, with no special characters or numerics.

The same error is given if the password is enclosed in quotation marks:

C:\>cctk --ValSetupPwd="obfuscated" --SetupPwd=newpassword
The setup password provided is incorrect. Please try again.

So I tried unsetting the admin password, with the same results:

C:\>cctk --ValSetupPwd=oldpassword --SetupPwd=
The setup password provided is incorrect. Please try again.
C:\>echo %errorlevel%
58

The error returned is consistently 58, which corresponds to the given error string in cctkerrorcodes.txt

The version of CCTK is the latest one available from the Dell site (downloaded 2018-07-05)

C:\>cctk --version

Dell Command Configure Version 4.1.0  478 (Windows - May  7 2018, 13:18:15)
Copyright 2009 - 2018 Dell Inc. All rights reserved.

and the BIOS is the latest available for the M3800 (A11).

There were suggestions in an earlier KB that the the codepage may have an effect, if it's not 437, so I've also tried modifying the codepage prior to running cctk, but the results were the same:

C:\>chcp 437
Active code page: 437

C:\>cctk --ValSetupPwd="oldpassword" --SetupPwd=newpassword
The setup password provided is incorrect. Please try again.

Adding a --LogFile= option to the invocation results in a single, rather unhelpful, log entry:

2018/07/05 16:40:01 cctk - The setup password provided is incorrect. Please try again.

There's nothing in the current release notes about this still being a problem.
Thoughts anyone?