I need a special debugging Tool!

I searched the Web and couldnt find anything appropriate yet. I have an application that only hangs on the PC of one Customer. I need something to write the Function Calls into a Logfile during Runtime, so the Customer can send me this logfile, for me to check where exactly it hangs.

May anyone can help me where to find such a tool?
Many Thx!

PS: Yes of course, I could myselfe include Output into a Logfile into my Classes. But I know there exists a nicer solution. Just need to find it.