There is no such thing as a portable application only applications that have been ported.
ACE is a plus there, as it is multiplatform. You must check where and how your type sizes are used. If ACE_* basic types are used you are hitting a streak there, as those are portable, else I would start by changing the Solaris version into using multiplatform data types and elements (use ACE facilities since you already have that in place).
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