The problem is with placing one
struts tag inside another. You can't do that.
Here's the good news: since you are setting the value of the hidden field yourself, you do not need the html:hidden tag because its only added value is in prepopulation... which you're doing yourself.
You can instead use:
<input type="hidden" name="filenamesave" value='<bean:message key="path.pictures"/>'/>
This will accomplish the equivalent of what you were attempting.