Create a performance counter with an instance name

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I use the following two lines of code to create a performance counter with an
instance name.

PerformanceCoun terCategory.Cre ate(m_CategoryN ame, "",
PerformanceCoun terCategoryType .MultiInstance, m_CounterName, "");

PerformanceCoun ter counter = new PerformanceCoun ter(m_CategoryN ame,
m_CounterName, "test", false);

But I get this exception:
"Category 'cat' is marked as single-instance. Performance counters in this
category can only be created without instance names."

Any idea?

Thanks.

Kai