[oe] ERROR: Please set the 'PERSISTENT_DIR' or 'CACHE' variable

[vivek tambakad]

Hi,
          I am building "bitbake x11-image". I get following error
ERROR: Please set the 'PERSISTENT_DIR' or 'CACHE' variable

I have set path correctly and infact build x11-image previously.
I installed some packages "php5 php5-cli php5-mysql mysql-server php-pear
php-db openssh-server" for
asterisk  application. Is the above installed packages create any conflict
with openembedded.
I am getting this error after installing these packages.

with regards
vivek tambakad