PxLoadImage problem

I have some problems using the PxLoadImage within a certain context.
I am using the PxLoadImage with a proper filled PxMethods_t structure, so
that I can use my own alloc, free, warning etc. just like it is shown in the
example of the help chapter.
The concrete problem is that if I am doing my calls to the PxLoadImage
before entering the PtMainLoop everything is working fine,
but if I want to call the PxLoadImage within a timer-event callback the
program is killed without any further error messages.
I am using log messages within the functions I support in the PxMethods_t
and none of these messages is shown.
If I have only some images the pre loading mechanism would work fine, but I
have to support about 600 Images so this would blow up my memory