IIRC, the error is caused by SYS(3) function generating repeating values on fast nachines. Try to replace SYS(3) with SYS(2015) as shown in the code below

* GENSCRNX.PRG
...
FUNCTION uniqueflnm
PRIVATE filename

DO WHILE .T.
  m.filename = '_' + RIGHT(SYS(2015),7)
  ***m.filename='_'+ALLTRIM(SUBSTR(SYS(3),2,7))
  IF .NOT.FILE(m.filename+'.DBF')
    EXIT
  ENDIF
ENDDO
RETURN m.filename

* END uniqueflnm
...

>
>I have an application written in Foxpro 2.6a for Windows.
>
>After making several modifications I try to build it and it appears to build but then crashes throwing a genscrnx error mode window on my screen and returning a "variable fscxbase not found".
>
>I am able to revert back to the old system and build it with no problem. I then copy the project file from that system into the updated system and again receive the same message. My guess is I am running out of resources, but I have no idea of how to address it.
>