mysql_upgrade.exe error when mysql is migrated to mariadb

Hi,

im migrating from mysql(5.1.73 64-bit) to mariadb 5.5.43 64-bit:
1. delete mysql/bin, mysql/share
2. unzip mariadb
3. update my.ini file
4. start MariaDB service
5. run mysql_upgrade.exe -u user -ppassword --port 3306 -f --upgrade-system-tables
and at this point i got the following error:

FATAL ERROR: Upgrade failed

The --upgrade-system-tables option was used, databases won't be touched.
Phase 1/4: Fixing views from mysql
MySQL upgrade detected
'""' is not recognized as an internal or external command,
operable program or batch file.

The migration has always worked. It has been not working since version 5.5.43.