I am not sure that this is a defect, since I am using puppet's fileserving for the first time and many other people seem to be using it without problems. However I have seen in the puppet-dev mailinglist, that someone else HAD the same (?) problem already.
I have set up a fresh /etc/puppet/ssl directory because of the error, have signed my client's key, but it didn't help.
I am running puppetmaster and puppetd on the same host, but this shouldn't matter, at least it didn't yet.
Used system is debian sarge.
I am appending my tar'ed ssl directory plus my fileserver.conf
Tell me if you need more information.
The output of 'puppetd -l console --test --verbose --debug':
[0;34mdebug: puppetd: Setting logdir to '/var/log/puppet' [0m
[0;34mdebug: puppetd: Setting vardir to '/var/lib/puppet' [0m
[0;34mdebug: puppetd: Setting rundir to '/var/run' [0m
[0;34mdebug: puppetd: Setting color to 'false' [0m
debug: puppetconfig/puppet/file=/var/lib/puppet/state/state.yaml: Autorequiring file /var/lib/puppet/state
debug: puppetconfig/puppet/file=/var/lib/puppet/state/state.yaml: subscribes to /var/lib/puppet/state
debug: puppetconfig/puppet/file=/etc/puppet/ssl: Autorequiring file /etc/puppet
debug: puppetconfig/puppet/file=/etc/puppet/ssl: subscribes to /etc/puppet
debug: puppetconfig/puppet/file=/etc/puppet/namespaceauth.conf: Autorequiring file /etc/puppet
debug: puppetconfig/puppet/file=/etc/puppet/namespaceauth.conf: subscribes to /etc/puppet
debug: puppetconfig/certificates/file=/etc/puppet/ssl/public_keys: Autorequiring file /etc/puppet
debug: puppetconfig/certificates/file=/etc/puppet/ssl/public_keys: Autorequiring file /etc/puppet/ssl
debug: puppetconfig/certificates/file=/etc/puppet/ssl/public_keys: subscribes to /etc/puppet
debug: puppetconfig/certificates/file=/etc/puppet/ssl/public_keys: subscribes to /etc/puppet/ssl
debug: puppetconfig/certificates/file=/etc/puppet/ssl/private: Autorequiring file /etc/puppet
debug: puppetconfig/certificates/file=/etc/puppet/ssl/private: Autorequiring file /etc/puppet/ssl
debug: puppetconfig/certificates/file=/etc/puppet/ssl/private: subscribes to /etc/puppet
debug: puppetconfig/certificates/file=/etc/puppet/ssl/private: subscribes to /etc/puppet/ssl
debug: puppetconfig/certificates/file=/etc/puppet/ssl/private/password: Autorequiring file /etc/puppet
debug: puppetconfig/certificates/file=/etc/puppet/ssl/private/password: Autorequiring file /etc/puppet/ssl
debug: puppetconfig/certificates/file=/etc/puppet/ssl/private/password: Autorequiring file /etc/puppet/ssl/private
debug: puppetconfig/certificates/file=/etc/puppet/ssl/private/password: subscribes to /etc/puppet
debug: puppetconfig/certificates/file=/etc/puppet/ssl/private/password: subscribes to /etc/puppet/ssl
debug: puppetconfig/certificates/file=/etc/puppet/ssl/private/password: subscribes to /etc/puppet/ssl/private
debug: puppetconfig/certificates/file=/etc/puppet/ssl/certs: Autorequiring file /etc/puppet
debug: puppetconfig/certificates/file=/etc/puppet/ssl/certs: Autorequiring file /etc/puppet/ssl
debug: puppetconfig/certificates/file=/etc/puppet/ssl/certs: subscribes to /etc/puppet
debug: puppetconfig/certificates/file=/etc/puppet/ssl/certs: subscribes to /etc/puppet/ssl
debug: puppetconfig/certificates/file=/etc/puppet/ssl/private_keys: Autorequiring file /etc/puppet
debug: puppetconfig/certificates/file=/etc/puppet/ssl/private_keys: Autorequiring file /etc/puppet/ssl
debug: puppetconfig/certificates/file=/etc/puppet/ssl/private_keys: subscribes to /etc/puppet
debug: puppetconfig/certificates/file=/etc/puppet/ssl/private_keys: subscribes to /etc/puppet/ssl
debug: puppetconfig/puppet/file=/etc/puppet/namespaceauth.conf: File does not exist
debug: puppetconfig/puppet/file=/var/lib/puppet/plugins: File does not exist
debug: puppetconfig/certificates/file=/etc/puppet/ssl/private/password: File does not exist
debug: puppetconfig/certificates/file=/etc/puppet/ssl/private/password: Changing mode
debug: puppetconfig/certificates/file=/etc/puppet/ssl/private/password: 1 change(s)
debug: puppetconfig/certificates/file=/etc/puppet/ssl/private/password/mode: File does not exist; cannot set mode
debug: Finishing transaction -742675018 with 1 changes
debug: getting config
debug: Loaded state in 0.00 seconds
debug: Calling puppetmaster.getconfig
err: Could not retrieve configuration: Certificates were not trusted: data too large for modulus
warning: Not using cache on failed configuration