Wago 750-841 IO Error

Hi everyone!
I have strange problem with my Wago device.
After power supply restart the I/O led indicator was start flashing on red.

And here is the problem.
Documentation says that should be 3 sequence of flashing:
first - quick flashing (10Hz) - mean start error message
second - should be error code
third - should be fault argument
In my case there is only 2 sequence.
After "start message" the IO led blink only 5 times and then repeat "start message" sequence.
What that mean?
I thought that in my case the error code is 5 and argument 0. I try to replace first module after power supply card and that won't help. Problem still exist.
What that mean? Did anybody have similar problem?

Ok i solved a problem.
I talk with 3 peoples from Wago support and only last of them give me a solution.
In my case error code was 5 and argument was 0. That mean general error in IO field bus after initialization.
Normally device should show what module is broken (error argument) but sometimes can't do it.
To find broken one i took off the last module (Terminator??) and place him after each one from existing module. Finally i find broken one. It was analog output module( 26's form CPU). Guy from support said me that i should do this operation (replacing modules) only when power supply will be shutted down.

Best regards and sorry for my English.
Michał

yep **** happens, sometimes even one module and a end module and then test each module apart is needed.
If a module can not communicate with base it is a problem to find.