AM335x BeagleBoneBlack Kernel booting-problem

Hi,
I've a BBB (BeagleBone Black) with an AM335x...

I tried to debian-Linux-kernels via Net-Boot with the u-boot-Bootmanager similar to these instructions:

or that one:

I try to boot different kernels using U-Boot, TFTP, ... over network - and I get strange results - I didnt understand what's happening... Instead of booting the kernel I see annoying reboots all the time (with different Kernel-Images!?!) - here an example:

The first rows are working fine (setting all the parameters in the u-boot-terminal ..., loading the images via network, ...) but then instead of loading the Kernel it crashes...
------------------------
U-Boot# setenv serverip 10.123.100.10
U-Boot# setenv ipaddr 10.123.100.12
U-Boot# setenv fdt_high ffffffff; saveenv
Saving Environment to NAND...
Erasing NAND...
Attempt to erase non block-aligned data
U-Boot# setenv kernel_addr 0x80008000
U-Boot# setenv fdt_addr 0x80f80000
U-Boot# tftpboot ${kernel_addr} uImage-new
link up on port 0, speed 100, full duplex
Using cpsw device
TFTP from server 10.123.100.10; our IP address is 10.123.100.12
Filename 'uImage-new'.
Load address: 0x80008000
Loading: *#################################################################
#################################################################
#################################################################
#################################################################
###################################################
1.6 MiB/s
done
Bytes transferred = 4560377 (4595f9 hex)
U-Boot# tftpboot ${fdt_addr} am335x-bb.dtb
link up on port 0, speed 100, full duplex
Using cpsw device
TFTP from server 10.123.100.10; our IP address is 10.123.100.12
Filename 'am335x-bb.dtb'.
Load address: 0x80f80000
Loading: *##
1.7 MiB/s
done
Bytes transferred = 23769 (5cd9 hex)
U-Boot# setenv bootargs console=ttyO0,115200n8 root=/dev/mmcblk0p2 ro rootfstype=ext4 rootwait
U-Boot# bootm ${kernel_addr} - ${fdt_addr}
## Booting kernel from Legacy Image at 80008000 ...
Image Name: Linux-3.8.13-rt9-00899-gd04fb13
Image Type: ARM Linux Kernel Image (uncompressed)
Data Size: 4560313 Bytes = 4.3 MiB
Load Address: 80008000
Entry Point: 80008000
Verifying Checksum ... OK
## Flattened Device Tree blob at 80f80000
Booting using the fdt blob at 0x80f80000
XIP Kernel Image ... OK
Using Device Tree in place at 80f80000, end 80f88cd8

Starting kernel ...

data abort
pc : [<8000800c>] lr : [<9f74c214>]
sp : 9f62ac90 ip : ffffffff fp : 9f7a34ec
r10: 00000000 r9 : 9f62af28 r8 : 9f6313a4
r7 : 00000000 r6 : 80008000 r5 : 9f7a7374 r4 : 00000000
r3 : 00005cd9 r2 : 80f80000 r1 : 00000e05 r0 : 9f62afe0
Flags: nZCv IRQs off FIQs on Mode SVC_32
Resetting CPU ...

resetting ...

U-Boot SPL 2014.04-00014-g47880f5 (Apr 22 2014 - 13:23:54)
reading args
spl_load_image_fat_os: error reading image args, err - -1
reading u-boot.img
reading u-boot.img
--------------------------

What's going on an the position "data abort" (~15 lines above)?
Does someone know the problem, has any good information, a link to an example, ...?!?
Thank's very much!