Intuit, for its part, was already reeling from disclosures last month that its Turbotax and Macintax programs contained flaws that, in rare cases, would create erroneous tax returns. Both programs are the best sellers for their respective personal computer systems -- Turbotax for computers that use the Microsoft Windows software operating system, and Macintax for users of Apple Macintosh computers. More than 1.2 million people used Macintax or Turbotax to prepare tax returns last year, according to Intuit. The company moved swiftly to correct the earlier errors, but the incident -- as well as revelations of potentially more serious flaws in a rival tax program, Taxcut, made by Block Financial Software Inc. -- shook the confidence of many personal computer owners who planned to use the software to prepare their 1994 tax returns. Intuit's troubles come as a merger agreement is pending with the Microsoft Corporation. That deal, announced last fall, calls for Microsoft to acquire the company for $1.5 billion.