i have found it, and i wish i can help anyone who finds the same problem... The cuestion is that when you call the CacheData function, you must care every value in the STGMEDIUM and FORMATETC structures. A good idea is to make something like this: ZeroMemory(pMedium, sizeof(STGMEDIUM )) and ZeroMemory(pFormatetc, sizeof(FORMATETC )) before beginning to give values to its members. You must remember too that since these two structures are passed to CacheData() they arent owned by aplication, that means for example that you can do :)something like this: pMedium = new STGMEDIUM; ...; ...->CacheData(...,pMedium, ...); ...; delete pMedium; because this will surely cause a program´s crash.:)