Security Error 2060:Security sandbox violation: ExternalInterface caller

Many a times we see such issues that we are not able to launch the application from html file and see the following error---

Security Error 2060: Security sandbox violation: ExternalInterface caller
file:///C:/Varun/myproject.swf
cannot access
file:///C:/Varun/myproject.html

So to avoid such a error you need to make some changes in html template html
In the HTML template make sure that the parameter 'allowscriptaccess' is set to 'always'

'allowScriptAccess','always',
param name="allowScriptAccess" value=“always"
if you are making a Object of swf from a flex application you can add the following parameter to the Object
swfObject.addParam('allowscriptaccess', 'always');

Cheers

Varun Rathore