Variable does not get assigned and no error is reported

Variable does not get assigned and no error is reported

Sorry that I can't provide an MWE, the issue is rather complex and
involves confidential data.
What I ask for, then, is enlighetnment as to how to debug this.
I have
<<SETUP,include=FALSE,cache=FALSE,echo=FALSE,warnings=FALSE,results='hide'>>=
<lots of database accesses, computations calculations>
BIG5TESTEXPORT <<- sqldf('select * from TEST,BIG5 where
TEST.Email_Address=BIG5.EMAIL')
BIG5TEST <<- cbind(BIG5,TEST)
@
If I process this with knitr, under a new R session, the variable BIG5TEST
is neither created nor assigned. BIG5TESTEXPORT, on the other hand, is.
Subsequent computation on BIG5TESTEXPORT proceeds as expected, whereas the
variable BIG5TEST is reported not to exist.
How do I debug this?
Any and all feedback appreciated.
Thank you,