Mikrotik script run once/twice and stop

Goodmorning,
first of all sorry for my english…

I need to “refresh” a NAT rule on my Mikrotik RB750GL every 30 minutes. For this purpose, i wrote a script with these lines:

/ip firewall nat remove numbers=2
/ip firewall nat add chain=srcnat action=masquerade out-interface=<ovpn-testvpn>

When i try to manually run the script it works first time; the second one too. And then stop. No log, no actions. Untill I reboot the RB.

Can you help me with this situation? I need to implement this script into a schedule. The schedule starts (the run counts increase), but it makes no actions.

Thanks in advance.

Do not use console numbers in scripts.