You can only use an iso once, if you use it multiple times it may corrupt.
-If you mess up your iso, delete it, and re-extract from the RAR`s.

* If the common/DLC is bigger than what is currently in the iso, overwriting will cause corruption.
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* Badly put together mods (Spaces/spelling mistakes/case sensitive writing)

* Inferior quality discs, you should use these to hotswap as a rule of thumb:
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* Altering a released set of mods, and doing it incorrectly (spelling mistakes and syntax errors)
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*Using the incorrect game disc region for your region.
(USA is Region 1/NTSC - UK is Region 2/PAL)

*Replacing DLC1 instead of DLC2

*Using WX360 instead on Xbox Backup Creator
(WX360 is for games Wave 2 and lower , XBC is universal)
WX360:
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Xbox Backup Creator:
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*Using DVD - R`s instead of DVD +R`s
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^^^ Wrong discs ^^^

*Extract the default.xex and then replace it again.

Hope this helps
credits goes to tim008
sticky please:D