gpg cannot connect to pinentry

Citing /usr/share/doc/gnupg/README.BUGS.Debian.gz:

gnupg: Piping content to gpg: echo foo | gpg --use-agent ... errors out with
       `gpg: cancelled by user'

    This might happen when gpg is unable to determine the correct name of the
    terminal. You can check the terminal given to the agent by running
    gpg-agent with the --debug-level advanced switch. The output might contain:

        gpg-agent[XXX] DBG: <- OPTION ttyname=/dev/tty

    whereas the output of tty says

        /dev/pts/X

    You'll have to set GPG_TTY to point to the correct terminal (see also
    gpg-agent(1)).

    Debian #359758 <URL:http://bugs.debian.org/359758>
    GnuPG #1047 <URL:https://bugs.g10code.com/gnupg/issue1047>

Setting your report to invalid. Reopen if the above doesn't fit your problem (but read the linked bug reports - they contain the explanation by the upstream author).

actually, it is not just, that i cannot connect from the terminal. the gpg-plugin of kmail from kde 4.6 beta is currently broken because of this issue!

You have not proven, that the "issue" you show on the cli is the same issue as in kmail! I gave you an explanation for the behaviour when piping content to gpg. You could at least verify this. And if someone thinks, this is the same with kmail, he should step forward and describe the issue. ATM this report contains nothing useful.

the issue that you describe show the error message:
gpg: cancelled by user

i have the error message:
gpg: Invalid passphrase; please try again ...
[snip]
gpg: no default secret key: bad passphrase
gpg: signing failed: bad passphrase

You do understand, that one error message is given by gnupg 1.x and the other by gnupg 2.x and that they might differ? Validate the issue by checking the verbose output of gnupg-agent (what you should have done already). I'll only examine this further, if you can say for sure, that you are not hit by the issue, that the terminal is not correctly determined. Bye.

i really like, doing beta tests, because of the friendly comments, that you get from maintainers, when trying to tell them about a bug related to their software.

there seem to be several people on the #kubuntu-dev channel, that have this issue. probably someone else will spent his time on this.