For C1 the officially acceptable max rate is 220 errors a second. IIRC, it is 1/hr for C2, but generally C2s are considered unacceptable.
From CDFreaks' media archive:
The error values are also displayed in the top area of the image. You will see the "max", "total" and "average" counts showing there. Max and total are the most important values, the average count is just that, an average of all the error values on the scan. It can be misleading sometimes, so don't fall into the trap of using the average counts as a measure of "quality". A disc can have fairly high average C1 value, and still be a very good burn.
In VERY general terms any C1 average count under 10 might be acceptable, but higher values are not always the end of the world either. But, on CDR's we prefer to see avarage C1 counts under 2, with max counts under 20.
Post your scans to CDFreaks' CD-R(W) Media tests archive. Be sure to read the posting guidelines thoroughly first.