overwriting SEH and debugging

[opexoc () gmail com]

Hello,

I am in situation that I have successfully overwrite SEH in some app. I know that because when I am debugging this app 
I get exception ( access violation ) and then I can thanks to go to fs:[0] find out what is in first SEH structure. 

I have overwritten this SEH by ordinary \xeb\x30\x90\x90 and address of POP edi/POP esi/RET 8 instruction in shell32 
module. I am wondering why when I press SHIFT+F9 in ollydbg I get "Debugged program was unable to process exception". 
But when I overwrite address of handler in SEH by for example: \x41\x42\x43\x44 then when I press SHIFT+F9 I get that 
0x44434241 cannot be accessed - so next exception - as it should be. Where is a problem?

opexoc