Any idea as to why I would get this error? I searched the forum and only found one other post and I'm not sure that the previous thread applies to me.

It could be the business object to which that browse dialog is bound.  Either you have a field with differing case between the different collections describing the field, or you have a custom property on the business object and you're trying to include it in the search fields. 

Looking at the code, the only dictionary referenced is the FieldDbTypes dictionary on the dictionary.  Check the BO at runtime and make sure that it contains a definition for every field that is contained within the search fields for the browse dialog.