I'm using Acrobat 8 / Windows 7. I've never had an issue signing a document until a couple of days ago. Now, when I 'place it', I immediately this this error:
Creation of this signature could not be completed.
Certificate parsing error:
Error encountered while BER decoding:
Since you mention "certificate" you are using digital signatures from the "Sign with certificates" group. Is this correct?
If so then have you used this particular signing certificate before? It looks like the certificate that you're using is corrupted. BER-decoding errors are very difficult to troubleshoot. They usually indicate some problem in the certificate.
You can check this certificate by going (in Acrobat XI) to Preferences->Edit->Signature->Identities&Trusted Certificates->More..., click on Digital IDs on the left panel, select your certificate in the right panel and click "Certificate Details" button on the top of the right panel. Then inspect your certificate in the Certificate Viewer if it comes up. If the certificate is corrupted the Certificate Viewer dialog may not come up.
Which Acrobat version (including minor) are you using? Which platform/OS?