[Framers] Conditional Expression build crashing FrameMaker with Internal Errors

[Lin Sims]

FM12, latest patch
Win 7 Pro, 64-bit (not sure if it has the latest patches, that's IT's issue)

I'm trying to build some moderately complex conditional expressions. At the
moment I'm trying to account for 6 separate conditions, with a probable 7th
in the offing, but every time I try to build an expression, FM crashes with
"Internal Error" messages.

Current conditions:

A
B
Internal
External
TBP (to be provided)
WriterNote

For all final books, the TBP and WriterNote conditions are never shown.

I have 4 books to produce. They all follow a similar pattern to this one,
which is what I'm trying to set up for the A+External set:

Condition

Appears

A

Y

Internal

N

External

Y

A+Internal

N

A+External

Y

B

N

B+Internal

N

B+External

N

At the moment, I've gotten the A+Internal expression working, but I can't
build A+External, and no, I haven't moved on to B yet because B is not
going out any time soon.

I believe the above table works out to the following expression, which is
what I'm trying to get into the Manage Conditional Text field:

("A" or "External" or ("A" and "External")) and not (("A" and "Internal") or
"B" or ("B" and "External") or "TBP or "WriterNote")

The problem arises when I try to enclose the second clause with its parens.
That is, I can get this far:

("A" or "External" or ("A" and "External") )and not ("A" and "Internal") or
"B" or ("B" and "External") or "TBP or "WriterNote"

but as soon as I try to enclose the entire "and not" clause in parens,
Frame crashes. The same thing happens if I enclose the second clause first
(it saves fine) and then try to enclose the first clause.

I tried editing in the MIF, but the entire expression disappears from the
pick list when I do that.

Any ideas on why Frame might be crashing? Any solutions? Is there a simpler
way of doing this? Do I even have the expression set up correctly?

<frustrated>
-- 
Lin Sims