VS 2010 debugger not loading symbols when attaching to NUnit

(I just posted this in the NUnit discussion group on groups.google.com)

Under VS 2008, I would run my tests under NUnit, and, if I needed to
debug, I would attach the VS2008 debugger to the running Nunit process
(Debug -> Attach to Process), and set any breakpoints on code I wanted
to examine. When I hit the Run buttion in NUnit, it would hit the
breakpoint. (BTW, if it matters, this was running NUnit 2.5.2).

I just upgraded to NUnit 2.5.4 and VS 2010. When I set a breakpoint,
then attach to NUnit, I get a little warning symbol on the breakpoint
dot, and hovering over it gives the tooltip "Breakpoint will not be
hit. No symbols are currently loaded". Going to the Debug -> Windows -> Modules window shows a whole bunch of Windows and NUnit modules
loaded, with the Symbol Status of "Skipped loading symbols", and then
1 module with a funny name that changes each time (r1euhmh5 right
now), and Symbol Status of "No symbols loaded". (There is no trace of a module with a name remotely like my DLL under test).

Right clicking the funny filename (assuming that to be some mapping from my
DLL under test), and clicking Load Symbols From -> Symbol Path, and
navigating to the bin\debug folder, then clicking the pdb file of my
DLL under test, I get the message "A matching symbol was not found in
this folder". (The top of the Open dialog box has a line that says
"Original location: r1euhmh5.pdb")

So what's changed? And how do I go about debugging/breakpointing
under VS 2010/NUnit 2.5.4 (Or is it possible I screwed something up
when I decided to go through my VS2010 options and set some of them to
more advanced levels than I knew what I was doing?)

I appreciate any help.