I think what's going on is that if excel can't intepret your formula as a formula it puts the double quote marks back after you've replaced them. When I use my own (valid) formulas it works. When I use yours it does not. The Dutch excel function names may be throwing me off a bit (ALS vs. IF) but for whatever reason you have the function calls for als and als.fout using semicolons to separate the parameters instead of commas.
"=als(Blad1!D6=0;Blad1!D7;data!G2)
"=als.FOUT(INDEX(dbase!E6:E9005;VERGELIJKEN(TEKST.SAMENVOEGEN(A1;A6;B6);dba se!L6:L9005;0));" ")
If I add code to first replace the semicolons with commas, then the 2nd replace will successfully replace the leading quote marks and excel sees the formula as a formula, at least on my version of excel (2010).
Selection.Replace What:=";", Replacement:=",", LookAt:=xlPart, _
SearchOrder:=xlByRows, MatchCase:=False, SearchFormat:=False, _
ReplaceFormat:=False
Sub B_Lokalen()
'
' B_Lokalen Macro
'
Range("A1:EI527").Select
Selection.ClearContents
Range("A1000:EI1526").Select
Selection.Copy
Range("A1").Select
Selection.PasteSpecial Paste:=xlPasteValues, Operation:=xlNone, SkipBlanks _
:=False, Transpose:=False
Application.CutCopyMode = False
Range("A1:EI527").Select
Selection.Replace What:=";", Replacement:=",", LookAt:=xlPart, _
SearchOrder:=xlByRows, MatchCase:=False, SearchFormat:=False, _
ReplaceFormat:=False
Range("A1:EI527").Select
Selection.Replace What:="""=", Replacement:="=", LookAt:=xlPart, _
SearchOrder:=xlByRows, MatchCase:=False, SearchFormat:=False, _
ReplaceFormat:=False
Range("A1:EI527").Select
Selection.Copy
Range("A1").Select
Selection.PasteSpecial Paste:=xlPasteValues, Operation:=xlNone, SkipBlanks _
:=False, Transpose:=False
Range("A1").Select
Application.CutCopyMode = False
'
End Sub