problems with secondary bootloader on LPC1768 with MCP1700

I'm using µVision 4.50.0.0 with Keil MCB1700 with LPC1768.

I wrote a secondary boot-loader, that reads srecord file from usb and writes that into flash starting 0x20000.
The AN10866.pdf from NXP helped a lot.

The application itself is built with following changes:
Target Options IROM1 Start 0x20000 Size 0x60000
Asm options Define NO_CRP.

The following code should start my application after
successful update/validating the present firmware:

#define APPL_RUN_ADDR           0x00020000

__asm void boot_jump(U32 address)
{
    LDR SP, [R0]
    LDR PC, [R0, #4]
}


void run_appl()
{
     SCB->VTOR = APPL_RUN_ADDR & 0x1FFFF80;

    boot_jump(APPL_RUN_ADDR);
}

This code snippet is copied from nxp's AN10866.pdf, too.

But the firmware doesn't start reliable. Where do I stuck?

APPL_RUN_ADDR is defined to 0x20000

at 0x20004 there's 00020229 (this is the Reset_Handler fro my application, which I checked in the map file).

Unfortunately I don't find the AN10866.zip example files, to see how nxp's bootloader was built exactly.

What else have I forgotten to do?

Thanks in advance
Hubert