%x was unexpected at this time. batch script

The problem is in your if %M% statement. Where is %M% ? declare it first eg

@echo off
set M=""
for /f "tokens=1,2 delims=," %%x in (file) do (
if %M% LSS %%x set M=%%x
)
echo Max X Value= %M%

Alternative, you can use vbscript

Set objFS = CreateObject("Scripting.FileSystemObject")
Set objArgs = WScript.Arguments
strFile = objArgs(0)
Set objFile = objFS.OpenTextFile(strFile)
t=0
Do Until objFile.AtEndOfStream
    linenum = objFile.Line
    strLine = objFile.ReadLine  
    s = Split(strLine,",")
    For Each num In s       
        WScript.Echo "num "&num
        If Int(num) >= t Then
            t=Int(num)
        End If  
    Next
    WScript.Echo "Max for line:" & linenum & " is " & t
Loop

example output

C:\test>type file
422,34464,55455,65421,88

C:\test>cscript //nologo test.vbs file
Max for line:1 is 65421

UPDATE: To find max value column wise

Set objFS = CreateObject("Scripting.FileSystemObject")
Set objArgs = WScript.Arguments
strFile = objArgs(0)
Set objFile = objFS.OpenTextFile(strFile)
t=0
Do Until objFile.AtEndOfStream
    linenum = objFile.Line
    strLine = objFile.ReadLine  
    s = Split(strLine,",")
    If Int(s(0)) >= t then      
            t=Int(s(0))
    End If      
Loop
WScript.Echo "Max is " & t & " (line: " & linenum & ")"

output

C:\test>type file
422,34
464,55
455,65
421,88

C:\test>cscript //nologo test.vbs file
Max is 464 (line: 2)