Good night.

I am having an annoying problem with a DLL.

Well, i needed to make a test with two different versions of a DLL on an application on IIS.

I renamed the original dll Primavera.ERPOnline.Bso.Proxy.dll to _Primavera.ERPOnline.Bso.Proxy.dll, and copy the new version to the folder.

After all the tests i removed the new dll and renamed the _Primavera.ERPOnline.Bso.Proxy.dll to the original name.

I made an iisreset, and try to initialize the application but for some reason i get an error, and i cannot start correctly the application:

Exception message: Could not load file or assembly '_Primavera.ERPOnline.Bso.Proxy' or one of its dependencies. The process can not access the file because it is being used by another process. (Exception from HRESULT: 0x80070020

What do i need to do to "delete" that referece to that dll?


  • Did you shutdown the server before renaming the dll file? – Khaled Nov 28 '10 at 8:02
  • As i remember, no. I made all without restarting. But now i have already restarted and the error remains. – Filipe Costa Nov 28 '10 at 22:05

Please check with this http://technet.microsoft.com/en-us/sysinternals/bb896645.aspx

  • This was not enough to solve the problem. – Filipe Costa Feb 3 '11 at 10:21

Please use the process explorer utility from sysinternals to check which process is using that file.


  • That's the problem Gaurav. I've already used it. But for some reason it never finds it! :\ – Filipe Costa Nov 29 '10 at 23:58
  • This is very strange. I delete the dll from the bin folder and it says that it doens't find the "Primavera.ERPOnline.Bso.Proxy". But, if i have the dll in the bin, what it doesn't find is the "_Primavera.ERPOnline.Bso.Proxy". – Filipe Costa Dec 1 '10 at 0:11
  • The process in use is System with PID 4. – Filipe Costa Feb 1 '11 at 18:25
  • You need to find using System Utilities what PID 4 is in your system?? – Gaurav Singh Feb 3 '11 at 20:13

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