Try the following code:

PRE

PROCEDURE cleanmemo
LPARAMETERS memotext
LOCAL newtext
m.newtext = CHRTRAN(m.memotext, CHR(13), ' ')
m.newtext = CHRTRAN(m.newtext, CHR(10), ' ')
m.newtext = ALLTRIM(STRTRAN(m.newtext, ' ', ' '))

IF .NOT. (m.newtext == m.memotext)
m.newtext = cleanmemo(m.newtext)
ENDIF
RETURN m.newtext

/PRE

test suggestion:
Create testing text in test.txt and run:

? '<' + cleanmemo(filetostr('test.txt')) + '>'

HTH