The invalid transaction handle exception goes like this (the second
exception happens immediately after first, while the third is during
shutdown of Project12.exe):

First exception:

Project Project12.exe raised exception class EIBO_ISCError with
message 'ISC ERROR CODE:335544569

ISC ERROR MESSAGE:
Dynamic SQL Error
SQL error code = -901
invalid transaction handle (expecting explicit transaction start)

STATEMENT:
TIBOInternalDataset: "<TApplication>.Form1.<TXtrimDataSetModule>.tblW
ebUser.<TIBOInternalDataset>'.


Second exception:

Project Project12.exe raised exception class EIB_ISCError with
message 'ISC ERROR CODE:335544727

ISC ERROR MESSAGE:
unassigned code


Third exception:

Project Project12.exe raised exception class Exception with
message 'This is a potential problem: 335544332'


Assigning IB_Session explicitly doesn't seem to help...
By the way, does IBO allow creation of IB_Session during run-time?