I have retried the manual method in a Virtual Machine running Win7 64bit (same as my PC) with the same binaries, keys and pbo file. That time the operation was successful. For the VM I did not set a password. My PC is an Active Directory domain member and I login using domain credentials. The VM is not a domain member.

Hello,

I already have seen this error years ago (~ 2008). If I recall correctly, there are two potential causes:

1. The most common is the usage of the public key to sign an addon but in our case, you can only select a private key.

2. A bit more tricky, 8009000b matches a Windows error, related to the account management which could corrupt the private key. What you could test would be to activate the Administrator Account, log into this account, create your signature and try to sign a file from this account and yours, to determine if its about the signature or the private key.

To enable the local administrator account, open a CMD as administrator and type:
net user administrator /active:yes
To disable it, replace yes by no.

Unfortunately I can't go down the local administrator route on this PC, it is an Active Directory domain member and I authenticate using AD user credentials. As I mentioned in my comment above, I was able to successfully sign the pbo using the same key and binaries when I ran it from within a virtual machine, so it doesn't appear to be the key that's at fault.

can acknoledge the problem:

Try to sing a file with DSSignFile and my biprivatekey on my domain-account (witch is part of the local administrator group) -> "cpaquire context failed"
Try to sing a file with DSSignFile and my biprivatekey on my local-account (witch is part of the local administrator group) -> worked totaly fine

Would be greate to have a solution for that!