CRM 2011. Solution import fails with error "An item with the same key has already been added."

Today I was helping to resolve following error during solution import: "An item with the same key has already been added".

I took traces and found following:

EntityService.Update caught exception: System.ArgumentException: An item with the same key has already been added.
at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
at Microsoft.Crm.Metadata.OptionSetService.GetExistingAttributePicklistInternal(Guid optionSetId, OptionSetType optionSetType, Nullable`1 optionValue, ISqlExecutionContext context)

Method "GetExistingAttributePicklistInternal" is retrieving picklist values from CRM and adding these values to a dictionary. It means that you have a problem with CRM instance you are deploying solution into.

I didn't have a chance to find a way how to fix this issue. We decided to use another environment for now and successfully deployed our solution.