Shell '%COMSPEC% /C "S:\SYMANTEC\SYMANTEC ENDPOINT PROTECTION 11 MR2 MP1\PATCH\SEP32_25TO333_CLIENTMSPMSI\MSILU.EXE" /P
 "S:\SYMANTEC\SYMANTEC ENDPOINT PROTECTION 11 MR2 MP1\PATCH\SEP32_25TO333_CLIENTMSPMSI\PATCH.MSP" /U /I
 "S:\SYMANTEC\SYMANTEC ENDPOINT PROTECTION 11 MR2 MP1\PATCH\SEP32_25TO333_CLIENTMSPMSI\SYMANTEC ANTIVIRUS.MSI"'

; -- Here is what you have today.. I have taken the liberty of breaking it in the smaller chunks
Shell '%COMSPEC% /C "S:\SYMANTEC\SYMANTEC ENDPOINT PROTECTION 11 MR2 MP1\PATCH\SEP32_25TO333_CLIENTMSPMSI\MSILU.EXE"
/P "S:\SYMANTEC\SYMANTEC ENDPOINT PROTECTION 11 MR2 MP1\PATCH\SEP32_25TO333_CLIENTMSPMSI\PATCH.MSP" /U /I
"S:\SYMANTEC\SYMANTEC ENDPOINT PROTECTION 11 MR2 MP1\PATCH\SEP32_25TO333_CLIENTMSPMSI\SYMANTEC ANTIVIRUS.MSI"'

; -- What I would recommend to do is to use Variables
$EndPoint = "SYMANTEC ENDPOINT PROTECTION 11 MR2 MP1"
$MSILOC = "SEP32_25TO333_CLIENTMSPMSI"

; -- So, now you should be able to simplify this quite a bit..

$CMD = '%COMSPEC% /C "S:\SYMANTEC\"'+$EndPoint+'"\PATCH\"'+$MSILOC+'"\MSILU.EXE"
$CMD = $CMD + '/P "S:\SYMANTEC\"'+$EndPoint+'"\PATCH\"'+$MSILOC+'"\PATCH.MSP" /U /I'
$CMD = $CMD + '"S:\SYMANTEC\"'+$EndPoint+'"\PATCH\"'+$MSILOC+'"\SYMANTEC ANTIVIRUS.MSI"'

Shell $CMD