Problem using digital signature in either oo 2.4/3.0

[napalmique]

Hello,

I went to instantssl.com, generated me a certificate, installed it, i can use it to sign emails, but whenever i try to sign OO documents, I fail:

I go to file/digital signature, in the window that pops up I click on add, it shows me the cert, i click on it, nothing happens, i click again, this time it adds it but it says the signature is invalid. also, when i open a document signed by someone else, it also tells me the signature is invalid.

I'm using fedora core 9 with OO 3.0, tried it with OO 2.4 but same result. Please help, I'm desperate...