There are some naming limitations of the *.cod files that you load onto a BlackBerry Smartphone.
Can you post up the name of the zip file you are using to pass to the Widget Packager? The *.cod file generated is based on the name of the zip used.
If you post up the zip file name we can see if you have any illegal characters in the name.
The "delete null" is a known issue on that Beta version of the simulator.
*.zip archive name is SRMInbox.zip.
When i build application first time, everything works fine. But when i rebuild application with same *.zip archive name (SRMInbox.zip) and try to upload it on simulator, i get NullPointerException. At the moment i'm simply changing *.zip archive name every time i rebuild application.
And on the simulator at the end of the day there is a lot of applications installed on it 
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Thanks about "delete null" information. But is there any valid way to delete application from simulator while it is running?
Are you loading the application through the "File -> Load Java Application"?
If so, after you have run your widget you can reset the simulator using the "File -> Reset" action. We have found that in that scenario the application is removed from the simulator. You can also get your simulator back to its original state by deleting any of the "*.dmp" files that exist in the simulator's directory.
Another way that I usually create my widgets, is use IIS/Apache to create a virtual directory to my widget's source. Then I make the "src" attribute of the <content> element point to the URL of my HTML file on my web server.
That way whenever I want to make a change to my widget, I just close the widget make the change on my local file and then re-open the widget. Essentially any scenario that forces a page re-load.
In this case you need to add the domain of your PC into the <access> whitelist. Then the only time you need to re-compile, is if you make changes to your config.xml file.
