Like I mentioned, I don't do much SOPC - designs, in fact I just dabbled a bit with it to find out out whether I could coerce/fit my interconnection scheme into an ST-compatible form which surprisingly worked out fine. But I haven't done a real SOPC-project yet.
I found the following in the Quartus II Handbook: Chapter 22: Avalon-ST Splitter Core
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Error Width : legal values 0–31 : Default 1 : The width of the error signal on the output interfaces. A value of 0 indicates that the error signal is not used. This parameter is disabled when Use Error is set to 0.
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