Please read the post "Steps to implement custom web services in SharePoint" before continue here.
I think, most of the people don't know about blocked file types and where can we set them. SharePoint by default, won't allow all the file extensions because of some security issues.
Why the SharePoint team didn't allow them by default. There is a strong reason behind it. i.e. not other than Security reasons. For example, EXE extension file, script files etc.
How to remove a blocked file type?
- Open central administration site.
- Go to Operations tab.
- Find a section named "Security Configuration".
- Under this section, you can find a link for "Blocked file types".
- On this page, you can see a text box area which displays all the file extensions one per line, which SharePoint blocked by default.
- You can edit and delete the extension. Then SharePoint allows user to upload the file or access the file.
So, if you are facing the problem of not able to upload the files of type .asmx, .exe, .chm etc.. This is the place where you set it. Happy SharePointing.