Pofibus problem between Siemens S7-400 and ET200S-IM dp

Hello. I need som help
I`m commissining a Siemens ET200S I\O rack with profibus communication between a S7-400.

And heres the problem:
When I download the project the ET200S DI\AI and DO modules works just fine.
But when I disconnect the power(24V) to the ET200S-IM and connect it back I just get "BF"(BUS-FAULT)on ET200S-IM.
Then I must emty the PLC and download the project again to re-establish profibus connection.

I hope some off you could have an answar

PS: I`m not an experienced programer sow, pleas use esay explanation.

This is correct as you have lost power to the ET200S. If PLC and ET200S were to power down and then back up together then the bus fault would go.
You do not need to download the program again. To clear the Bus fault turn the key in the PLC to Mres. then back to run. If this does not clear then you must look at the stack and in your program when comms is reestablished clear the error bit.
This is normally useful if a profibus node fails the PLC will then fault - one can set the comms time out.

Thanks for rapid response.

The PLC dos not go in fault, just the ET200S. The Bus-fault alsow hapend when PLC and ET200S were to power down and then back up together. And it dos not help to turn the key to "Mres" and back to "Run".

Sow I think its a parameter or somthing that makes this happens, but i do not know where to look or what to look for

Problem solved

Just informing that the problem is solved.
It turns out that the Backup-battery in the PLC was emty and the ET200S was removed from the HW at every power loose..