dpkg

hello,
i am confused.
i created a package like the howto said. with control file and so on. i build it with dpkg --build testpaket. testpaket.
the result was testpaket.deb

Now the installation.

# dpkg -i testpaket.deb

(Reading database ... 92720 files and directories currently installed.)

Preparing to replace bz-losetup 1.0 (using testpaket.deb) ...

Unpacking replacement bz-losetup ...

dpkg: error processing testpaket.deb (--install):

package control info rmdir of `opt' didn't say not a dir: Directory not empty

Errors were encountered while processing:

testpaket.deb

(Important - the package was not build from the source - building from source and installation is fine)

three month ago, i build packages with dpkg -b ...
And the installation was fine. what's wrong?

thx for help