Here are steps to resolve this issue:

1 – Open regedit (Type regedit in Run)
2 – Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\ShellIconOverlayIdentifiers;
3 – Rename last few entries OR unused entries by prefix ‘z_’ to it. I renamed all Dropbox entries to z_DropboxExt1, z_DropboxExt2, z_DropboxExt3 on my PC.
4 – Log off OR restart PC

I have resolved on: Windows 7 32 bit + TortoiseGit 1.6.5.0

It may works on Windows Vista and Windows 7