Sounds like the derailleur doesn't have enough chain wrap to handle the gear range you want to use. That means you'll need a derailleur with a longer cage to handle the extra chain wrap.


Calculate your chain wrap like this (Large Rear Cog + Large Front Chainring) - (Small Rear Cog + Small Front Chainring)...for you thats (32+46)-(??+26)

without knowing your small cog size (in teeth) I'd venture a guess that you'll need a Rear Derailleur with at least a 40 Tooth capacity, and it will need to handle a cog of at least 32. Shouldn't be too hard to find.