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>> That DLL is built in Release mode. So practically, all allocations/deletions are done in the same DLL and memory context.
...
>> dbgdel.cpp(52): _ASSERTE(_BLOCK_TYPE_IS_VALID(pHead->nBlockUse));...

What boost libraries are you using? If UTF, are you using auto-linking?
http://www.boost.org/doc/libs/1_45_0/libs/test/doc/html/utf/compilation.html#utf.compilation.procedured
Using a release boost...

>> I discovered that the problem happens only when that DLL is compiled in RELEASE while the main application is compiled in DEBUG.
Sounds like memory is being allocated in one module, and freed in...