I believe that you are recognize as user nobody so it will not let you write...
a quick workaround for VM datastore will be to set anon=0 on the export policy
you can do so by modifying the export poilcy rule:
export-policy rule modify -vserver SVM -policyname EPol -ruleindex 1 -protocol any -clientmatch 0.0.0.0/0 -rorule any -rwrule any -anon 0
Hope it will help 😉