Problems with scriptable plugins

I've written a scriptable plugin for Mozilla using the API described at
http://www.mozilla.org/scriptable/.

My plugin is working perfectly apart from on fault.  If the HTM used to load
the plugin does not contain the statement:

var embed = document.embeds[0];

Netscape will produce an error:

"The Plugin performed an illegal operation.  You are strongly advised to
restart Navigator"

After a lot of testing, I tried omitting this line from the sample files
(Simple and Scriptable) supplied with the Mozilla code, and they suffer from
the same problem.

My plugin does not need to be scripted, so it is important that it does not
fail if scripting is unused.

Thanks in advance
Dan