.xmodmaprc not quite working

Here's my .xmodmaprc, with trouble lines in bold:

Code:

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! -*- comment-start: "!" -*-
! make capslock behave like control
remove Lock = Caps_Lock
add Control = Caps_Lock
keysym Caps_Lock = Control_L

! make left control behave like hyper
remove Control = Control_L
! this line is troublesome
! add Mod3 = Control_L           
keysym Control_L = Hyper_L Hyper_L Hyper_L

! make right alt behave like backspace
! this next line doesn't work but doesn't error
remove Mod1    = BackSpace   
remove Mod4    = BackSpace
! depressingly, putting this next line before the previous two makes the "remove Control = Control_L" line not work
keysym Alt_R = BackSpace BackSpace BackSpace

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The commented-out "add Mod3 = Control_L" causes the following error when not commented out:

Code:

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X Error of failed request:  BadValue (integer parameter out of range for operation)
  Major opcode of failed request:  118 (X_SetModifierMapping)
  Value in failed request:  0x17
  Serial number of failed request:  18
  Current serial number in output stream:  18

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Right now I manually finish the job with xkeycaps every time I start X. I don't have much hope that I'll get xmodmap to work properly, but perhaps someone knows something?

Just to be less of a DenverCoder9, here's my new working version:

Code:

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! -*- comment-start: "!" -*-
! make left control behave like hyper
remove Control = Control_L
keysym Control_L = Hyper_L
clear Mod3
clear Mod4
add Mod3 = Hyper_L

! make capslock behave like left control
remove Lock = Caps_Lock
keysym Caps_Lock = Control_L
add Control = Control_L

! make right alt behave like backspace
remove Mod1 = Alt_R
remove Mod4 = Alt_R
keysym Alt_R = BackSpace BackSpace BackSpace

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