this is error in your script
in change log you could read that no in find clause you have to use string in quotes
/ queue simple remove [/ queue simple find interface=all]
this will look for variable called all and when it does not find any variable with such a name it will be substitured with "" (nothing) and then report you what you have,
instead you have to use quotation resulting in
/ queue simple remove [/ queue simple find interface="all"]
so, if you use string after find or find where clause it will be considered to be a variable name not the string if the variable does not exist.
actually this is more like any other scripting language where you have to put string in quotation to use it as a string.
please note this change, as everywhere you use find you have to make changes in the script code
also setting code like this will work
:global all all
/ queue simple remove [/ queue simple find interface=all]
that way you create global variable all that contains value of string all and when you set it in your script it can resolve to the value of variable all to the string value all.