You can't nest one custom tag inside another, so what you've written is invalid.
Also, looking at your code, it looks like you're probably iterating over a list and creating a collection of related checkboxes. If this is the case,
you should be using the html:multibox tag, rather than html:checkbox.
Here's what I'd recommend to fix it. Putting something in the body of a html:multibox tag is another way of specifying a value attribute. So, the following should work:
Note that in this case the
check property should be of type
String[].