Windows 7 Phone Error: Can't connect to your phone. Disconnect it, restart it, then try connecting again

I recently got this error after I changed my computer name. There are a bunch of different ways you can end up with this. The solution that worked for me is listed below:

It seems that you are having problems with your personal digital certificates! I'd suggest you to create a new certificate as described in KB 2468307 and the steps below:

1.	If it is running, close the Zune software and disconnect your phone.
2.	Open Certificate Manager. To do this, click Start, type certmgr.msc, and press Enter.
3.	Expand Personal, and then expand Certificates.
4.	Click the heading for the Issued By column to sort the column, and then look for one or more certificates that is issued to "zune-tuner://windowsphone/...".
5.	Right-click that certificate and then click Delete. Click Yes.
6.	From the File menu, click Exit.
7.	Click Start and in the search box enter %userprofile%\Application Data\Microsoft\Crypto\RSAand click OK.
8.	Find the folder that begins in "S-1-5-21-".
9.	Right-click the folder and then click Rename. Rename the folder so it ends in .bak.
10.	Start the Zune software and connect your phone to create a new certificate.

Please keep me informed if this procedure helped you out to resolve this issue.


Source: http://answers.microsoft.com/en-us/winphone/forum/wp7-sync/trying-to-connect-a-windows-phone-7-samsung-focus/fc7b885e-e069-4426-958a-84816e8a19e4