Do you get any error when the second install crashes? I think your best bet is to uninstall the second version and start over.
I think you should create a new folder somewhere else. Did you create the folder in your C: drive? Maybe create a folder at "C:\Program Files\FXCM MT4 powered by BT" called, "MT4 - Second Installation".
After you create the folder, you can
download MT4 with this link.
During the installation, change the installation destination to the new folder on your computer. For example, delete, "C:\Program Files\FXCM MT4 powered by BT" from the Installation Folder field and click Browse to locate the "C:\Program Files\FXCM MT4 - Second Installation" folder.
Next, change the name of the Program Group. Manually enter the name of your new folder "MT4 - Second Installation" and click on "Next".
After you finish, then try to launch the second version and let me know how it works! You should be fine though.