What's WRONG with this sentence?

it should be

In addition, Fincham (1999) indicates that the majority of research regards consultants as a group of people who are outside of the organizations.

In addition, as Fincham (1999) indicates, consultants have been regarded by the majority of research as a group of people who are outside the organizations.

OR

In addition, Fincham (1999) indicates that consultants have been regarded by the majority of research as a group of people who are outside the organizations.

However, I think that the sentence reads awkwardly with "regarded" in there. Usually, people regard things. In this case, you are saying that research regards something. Try using "proven by the majority of research."

Try this

In addition, as Fincham (1999) indicates, consultants are regarded as a group of people who are outside organisations, by the majority of research projects conducted in this area.

It should not say "as Fincham..." it should just say Fincham. But I like your "in addition". Continue to use conjunctions where appropriate.

try to cut down on the use of "that" and the verb "to get"

Present tense is simple and sounds best.

Unless you are American and can't grasp the language and have to make it simpler organizations > organisations.

I think it should be...

In addition, Fincham (1999) stated consultants are regarded by the majority of researchers as a group of individuals who are seperate from the internal organisational environment.

How does that sound?

It's an incomplete sentence; the idea doesn't fully come across. You could say, "In addition, Fincham (1999) indicates that consultants have been regarded by the majority of research as a group of people who are outside the organizations" (just take out the "as").

it doens't make sense.

I think it should read

In addition, as Finchman (1999) indicates, consultants have been regarded by the majority of research, as a group of people who are outside the organizations.

Well, it's got some comma splice and other grammatical problems (I would also recommend getting rid of the "state of being verb" as it is in the passive voice and very bland here -- use "operate outside of the organizations" or something). Here is your sentence slightly modified:

In addition as Fincham (1999) indicates, consultants have been regarded by the majority of research as a group of people who are outside of the organizations.

In addition, as Fincham (1999) indicates, consultants have been regarded by the majority of research, as a group of people who are outside the organisations.

In English, rather than American, and utilising one or two more comma's.

Edit ; Paganmum is also correct (though spells with a "z"), and has a different meaning.

I suppose it all depends on what you are trying to say.

Change the puctuation and adjust as below and it will make more sense:

In addition, as Fincham (1999) indicates, consultants have been regarded by the majority of research(ers?) as a group of people who are outside the organizations.

I would write it as:

Drop the "as"

Additionally, Fincham (1999) indicates that consultants have been regarded by the majority of research as a group of people who are outside the organizations.

or

Drop "that"

In addition, as Fincham (1999) indicates, consultants have been regarded by the majority of research as a group of people who are outside the organizations.

Even when fixed, it sort of seems like an unnecessary statement, as consultants are commonly people from outside of the organization, brought in to be objective.