The auditor did not accuse the S.E.C. of cooking its books, and the mistakes were corrected before its latest financial statements were completed. But the fact that basic accounting continually bedevils the agency responsible for guaranteeing the soundness of American financial markets could prove especially awkward just as the S.E.C. is saying it desperately needs money to increase its regulatory power.That has ominous implications for investors. The S.E.C.’s technology systems, for example, lack the ability to perform sophisticated analysis of large batches of financial material. As a result, a Congressional report says, S.E.C. analysts sometimes resort to printouts, calculators and pencils. While investigating the “flash crash” of May 6, 2010, S.E.C. computers were so strained by the crush of data from just one day of trading that it took three months to figure out what had happened.