MTS debugging

hi..
actually i have been asked this question in an interview..

they asked...say i have some dlls stored in a MTS...and different clients(.exes) are trying to access different dlls. Out of the dlls, i could figure out that one dll is taking around 100% of CPU time...and other clients are also complaining that, they are not able to access their programs.How can u debug that particular dll and tell what is the error in it...mind it when i told i have to stop its from running to find out the error, they simply gave a laugh...
hope to listen early from u..

thanking U
Pradeep