Incremental Updates and PKCS7 Signatures

Hello, this is my first message in this forum and I thank you in advance for your help.

I am developing a component to countersign PDFs. I was able to place the first signature ok, but when a countersign it problems come.

The way I countersign the document (as i read in the document "Digital Signatures in the PDF Language") is:
I create an incremental update with the following information:
1* Catalog changes
2* Info object
3* Acroform changes
4* New Annotation
5* New signature.
6* xref section
7* Trailer
The new signature is computed on the whole document but the signature new itself.

After this, not only the new signature is invalid, the previous signature becomes invalid althout there is no change in the previous version. I only have to remove the incremental update to get first signature to be valid again.
Acrobat Reader shows next message:
--
Error during signature verification.
Unexpected byte range values defining scope of signed data.
Details: byte range of signature is invalid.
--

I have reviewed thouse ranges several times but i did not find any error. Can anyone help me?
I could post a (badly) countersigned file if that could help.

Thank in advance,
José