IPSEC service fails to start with Error 2: The system cannot find the file specified

This might be caused by one of the registry entries failure.. IPSec needs to be rebuilt to fix the issue. Follow below steps if it fixes..

 To rebuild IPSEC, follow these steps:

1. Click Start, click Run, type regedit, and then click OK.
2. In Registry Editor, locate and then click the following subkey: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\IPsec\Policy\Local.  (In my case, the server’s registry ended before IPsec.  If this is the case, skip to step 6.)
3. On the Edit menu, click Delete.
4. Click Yes to confirm that you want to delete the subkey
5. Quit Registry Editor
6. Click Start, click Run, type regsvr32 polstore.dll, and then click OK.   

If the IPSec service fails to start, you may see the machine is not communicating with any other network, may not get the IPaddress from DHCP and etc.,

SQL Server 2008 R2 installation fails

Installation wizard says 2005 tools should be uninstalled even after uninstalling all 2005 components

This is due to some add-ons installed for SQL Server 2005.

Here is the solution I found somewhere I don't remember: (Thanks to the author and I am sharing further)

1. run Regedit

2. Check HKLM\SOFTWARE\Microsoft\Microsoft SQL Server\90\Tools\ShellSEM
3. If it exists, rename "ShellSEM" to anything

4. Run SQL server 2008 installation again