Lots of free and helpful Internet resources (hosted DOC, supplemental technical and conference topic-related papers) at the SAS support website
http://support.sas.com/ -- consider using the Google search mentioned below.
Also, if necessary, suggest you most your SAS log output with the diagnostic messages (and code) leading up to the error, particular about the INFILE and that file which you must have allocated elsewhere?
Also, for future reference, helpful info about your SAS version, OS platform, whether the program has or has not worked previously (is it new function), whether SAS is installed locally on your machine or on a remote server.
Scott Barry
SBBWorks, Inc.
Recommended Google advanced search argument, this topic / post:
+"file in use" site:sas.com