[ubuntu-in] synaptic package manager error

[ambika divya]

This is the error message with synaptic package manager whenever i trying to
open that ...........

E: dpkg was interrupted, you must manually run 'dpkg --configure -a' to
correct the problem.
E: _cache->open() failed, please report.

Please explain whats the problem and how to fix it .
When run this .....'dpkg --configure -a' says command not found ....
I am really new to linux ,please explain me simply .
Thanks.
-- 
ambika....................
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