I have the same problem on my portal.

 

If I delete the ICSharpCode.SharpZipLib.dll, the File Manager works. BUT the file operations in the editor give me errors. If I bring the ICSharpCode file back to the bin folder, the file operations in the editor work again.

 

Here's what I did. I uploaded some icon files through a zip file via the DNN 4 File Manager. With ICSharpCode present, the File Manager does not work. I deleted ICSharpCode and the File Manager did work. Once the icons were loaded, I went to the editor to use the icons in my web page. Clicking the "Insert Image" icon in the editor created an error. I restored the ICSharpCode to the bin folder and the Insert Image in the editor worked again.

 

I can keep doing this if I have to, but I really don't want to go back and forth deleting and restoring the ICSharpCode file. Any suggestions?