No ruleset for ORDERS/96A available when receiving EANCOM message with B2B AddOn AS2 adapter

When receiving an edi message via AS2 adapter of SAP B2B AddOn with following data:

UNB+UNOC:3+GLN1:14+GLN2:14+150610:1057+3121212+++++EANCOM'

UNH+1+ORDERS:D:96A:UN:EAN008'

Following exception is thrown:

Unexpected Error occured while processing the AS2-message: Cannot deliver message to Moduleprocessor, cause: Error in conversion

of ORDERS/96A-Edifact-Document at character 515 to XML: java.lang.UnsupportedOperationException: No ruleset for ORDERS/96A available.

But the data is available in B2B tables (control key SAP type ORDERS version 96A and control key SAP-EANCOM type ORDERS version 96A and

SubVersion EAN008).

Only one calling client is having the problem. Using another test client results in correct order processing. Also using a file adapter to pickup the archived (payload after decryption) edi message results in correct order processing. Any ideas what may be the problem?