It is a permission issue.
https://wiki.multitheftauto.com/wiki/Server_Commands#aclrequest
First verify if the meta.xml has any acl request listed in it's meta.xml
/aclrequest list <resourceName> all
And if loadstring is listed, grand permission.
/aclrequest allow <resourceName> all
If not listed, add it to the meta.xml of the resource:
<aclrequest>
<right name="function.loadstring" access="true" />
</aclrequest>
See example: https://wiki.multitheftauto.com/wiki/Meta.xml
Run:
/refreshall
And try the aclrequest commands again.