Error cannot open Packages index using db3

[Pellegrini Giuliano <gp1 ideainformatica com>]

 Hi all,

I have created a simple rpm, but I have a problem with %post.

My spec file is :

...

%post

rpm -q sendmail

I can build the packeges but when I try to install with rpm -ivh I have
this message:

cannot get shared lock on /var/lib/rpm/Packages

cannot open Packages index using db3 - Operation not permited(1)

--> The rpm database cannot be opened in db3 format.
    If you have just upgraded the rpm package you need to convert
    your database to db3 format by running "rpm --rebuilddb" as root.

If I comment the line:

rpm -q sendmail in the %post section, I haven't nothing errors.

Where is the problem ?
Is impossible to call a rpm query in the %post section ?

Thanking in advance and sorry for my english.

Pellegrini Giuliano.