[plt-scheme] cross-module compile problems

I am trying to isolate a small block of code that replicates my (or the 
compiler's) issue. So far not successfully. I am using version 4.2

I have -- module a requires module b
module b does (provide (all-defined-out))
It runs fine in the interpreter. But fails to compile. It gives the 
following error, listed below. "file-name" is the first exported proc 
that is encountered.

 >>>
projects/scheme/itemizer/a.scm:28:7: compile: unbound identifier in 
module in: file-name

 === context ===
/home/geoffrey/plt/collects/compiler/embed-unit.ss:366:4: get-code
/home/geoffrey/plt/collects/scheme/private/map.ss:44:11: for-each
/home/geoffrey/plt/collects/compiler/embed-unit.ss:743:4: 
do-write-module-bundle
/home/geoffrey/plt/collects/mred/private/mrmenu.ss:244:17: command 
method in basic-selectable-menu-item%
/home/geoffrey/plt/collects/scheme/private/more-scheme.ss:155:2: 
call-with-break-parameterization
/home/geoffrey/plt/collects/scheme/private/more-scheme.ss:271:2: 
call-with-exception-handler