3rd edition porting problem

[novis]

Hi Forum,
I do have an application which is using a background picture.
On my 2nd Edition N70. For an easy installation I put the picture via *.pkg into the sis-file and everything worked fine.

My very first step in porting my application to 3rd Edition was to put the background pic manualy (just to try out) to the same folder as it was on my 2nd edition N70 (which was c:\system\apps\myapplication\background_pic.png).
The test via python script shell on my 3rd Edition N73 was fine. (no problems so far)

Second step was to use ensymble to create and sign my application.sis.
After successfully installing the application on the N73 and starting it, I realised that my application obviously could not find the background pic anymore.
If I start the same application from the script shell it can find the background pic.
In my application i used the following syntax:

self.background=graphics.Image.open('c:\\system\\apps\\myapplication\\background_pic.png')

so where is the problem?
can someone give me a hint?
thx