If the calculation option has been set to automatic, change it to manual. Doing so will also prevent the workbook from recalculating the values and this can make file accessible. For this, Click ...

In interactive mode, if you issue a FILENAME statement or function or attempt to allocate a file with the FNAME window for a file that does not exist, and if you do not specify DISP=NEW, and if the ...

specifies the physical name of an external file. The physical name is specified so that the external file is recognized by the operating environment. The FILENAME statement associates a SAS fileref (a ...