Visual studio is waiting for internal operation to complete

For VS2015 users who are dealing with this problem: close everything, delete the ".vs" folder on the project root and reopen it.

There are also some steps, like to clean different cache you can follow, but it hasn't solved my problem… Check this blog post.

The important part of it:

There could be many reasons behind this. Few common fixes are below:

1. Remove website cache from following location: C:\Users\%USERNAME%\AppData\Local\Microsoft\WebsiteCache
2. Restart IIS: Start → RUN → iisreset
3. Go to Tools → Options and browse all the options and disable all unnecessary options.
4. Clear cache.
5. Remove temp files.
6. Ensure there is enough space in C (System) drive.

Update 2017-01-03
There are also ASP.NET caches in C:\Windows\Microsoft.NET framework folders, but this is rather for website or debug cache problems. When in the mentioned folder, search for "Temporary ASP.NET Files" in sub-directories and delete their content. If some files are locked, then iisreset should help.