Invalid library (maybe not a PHP library) error

Hello,

On Loading my PDO-interface based driver, PHP gives the error:

"PHP: Startup: Invalid library (maybe not a PHP library) 'php_pdo_xyz.dll in
unknow on line 0 "

I wrote a PDO-based driver, modelling the code on lines of  SQLite driver.
Compiled my driver as Dll , added the extension to php.ini. on running PHP,
I get the above err .

To add: I used DependencyWalker tool to see if I have missed some Dll, I
find that tools seems to find my Dll fine.
The output list of Dll pdependancies of my driver-Dll looks exactly like
that of php_pdo_sqlite.dll

Please let me know, where could be the potential problem.

thanks,
-sanjeev kumar