I had a customers computer be locked on SafeSearch.ch as the default search provider. These are the steps I was able to take to fix the problem. The machine I was working on was windows 7 Home 64-bit
Navigate to C:\Windows\System32\GroupPolicy
Open each subdirectory there and change the *.pol files to *.sav, E.g. registry.pol becomes registry.sav.
Hit Windows-Key + R, type the following in the box and hit enter
reg delete HKEY_LOCAL_MACHINE\SOFTWARE\Google\Chrome
In the command promt window that opens type: Yes and press Enter.
Restart Google Chrome and check whether you can change the search engine.
Here is a screen of what you will see in chrome settings