Error in IDOC Adapter Processing

Hello,

I'm testing the IDOC adapter on a PI 7.3 system in a simple file-to-IDOC scenario. I'm reading material master data from a XML file and send it to an ECC 6.0 system. The file processing is working fine, but after that I get an error in SXMB_MONI. It says there occurred an 'Error in IDOC Adapter Processing'. The detail message in the monitor looks like this:

<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>

-<!-- Call Adapter -->

-<SAP:Error SOAP:mustUnderstand="" xmlns:SAP="http://sap.com/xi/XI/Message/30" xmlns:SOAP="http://schemas.xmlsoap.org/soap/envelope/">

<SAP:Category>XIAdapter</SAP:Category>

<SAP:Code area="IDOC_ADAPTER">ATTRIBUTE_IDOC_METADATA</SAP:Code>

<SAP:P1>I::000</SAP:P1>

<SAP:P2/>

<SAP:P3/>

<SAP:P4/>

<SAP:AdditionalText/>

<SAP:Stack>Error: I::000</SAP:Stack>

<SAP:Retry>M</SAP:Retry>

</SAP:Error>

I already checked ST22, everything is ok there - no errors. Does anybody know this issue?

Thanks in advance!

Regards,

Václav