error searching a list "There are too many results for this search. Please try your search again"

I'm searching a list on my sp2010 enterprise farm (we do not have FAST) - it is a small list currently (only 6 items) but when I search for a short string with a wildcard "ac*" I get the error text: "There are too many results for this search. Please try your search again with more specific keywords. "

If I add another character "ac1*" then I do get results

I've tried this on a different list in a different site collection and the 2 character search works (the other list has several thousand items, and my search returns about 150 results)

the ULS log shows below, in addition to the error about too many results

<msgtype>HandleRequest</msgtype><ErrMsg>The query was too complex to be executed. 0x80041606</ErrMsg><HR>0x80041606</HR>

any suggestions?