Digital Signature not working for self extracting packages.

[shirome]

I want to create a Digital Signature for my Self extracting exe (i.e Single file executable).
I want to use isign.exe so that I can supply my password as a parameter when using in command line.

But when I used isign.exe with the following command

>"C:\Program Files\InstallShield\Professional 7\Program\Bin\isign.exe"
-spc "D:\source\mycert.spc"
-v "D:\source\mykey.pvk"
-p "MyPwd"
-cp "Microsoft Enhanced Cryptographic Provider v1.0"

The executable size changes and it returns "succeed", but when I look at the file properties
the Digital Signature tab is missing.

But if I used any of the techniques given below it works fine.
a) Using the editor i.e Specifying .spc and .pvk file Sign tab in Media properties.
b) Using the signcode.exe with the .spc and .pvk files.

Therefore I am pretty sure that spc file, pvk files and password are correct.

I am using Install Shield professional on Windows XP. I have all the latest updates for install shield and
windows.
I really appreciate any help

Thanks in advance
Shirome