gnupg problem "no pinentry"

[joerg van den hoff]

maybe someone knows what is going on here:

for some time know (since whenever `gpg' started to use this litte pinentry GUI for querying pass 
phrases) I have the rather sporadically reappearing situation that gpg interaction fails with a "no 
pinentry" error.  this always happens out of the blue after weeks/months of problem-free behaviour.

the only way I have found to get it work again is reboot (this concerns machines which are usually 
running 24/7) ...

question: is this a known problem? why is gpg suddenly no longer able to find the pinentry app to 
use (as it seems is the case -- or is it a problem of the pinentry app itself??)? can/should I fix 
it via some configuration setting?

thanks
joerg