Question: I'm trying to `svn update` my SVN working copy with TortoiseSVN but the update fails, asking to perform the clean up first.

However, the `svn cleanup` fails too stating that a `\.svn\pristine\20\20long-namecbf.svn-base file cannot be found`. 

I've already tried to release the lock but this does not work either.

**Any idea how should I proceed?**

Answer: 
I solved this by

1. Creating an empty file 
/workingdirectory/.svn/pristine/da/da39a3ee5e6b4b0d3255bfef95601800afd80009.svn-base
2. Run **svn cleanup**
You can use [SmartSVN](http://www.smartsvn.com/) to restore lost pristine file.

Download and install it. It's not free but 30 days free trial should be enough to repair your repository. 

Open your working copy in **SmartSVN**. To repair, select ***Modify*** > ***Validate Admin Area...***

Enjoy!