If I try to preview the grid I got the following error:

E:\xampp\htdocs\Hemtst\components\com_grid\GridConfigManager.php on line 101

JError Can't load database driver

Is it possible, that there are some old tables left in your joomla database? If so, you should uninstall component, manually drop tables named yourprefix_grids and yourprefix_grid_conn, and than install your component again. Or contact us by e-mail, because I have just prepared a package that does it all.

About database driver error: make sure your oracle and mssql drivers were installed to libraries/database/database/, and second: you should write for database type 'oracle', 'mssql' or 'mysql' or 'mysqli' and nothing else. But this is rather connected to the first problem if my guess is correct.

It's working, I'm not sure what did the trick, but its working. I uninstalled the component and made sure no old stuff was left behind. Then I completely unpacked the downloaded file. After this I copied all files in the componets database directory to libraries/joomla/database/database/ and installed the component again. Now it works fine. Thank you for your help.