That approach will work OK only if Skype has allready been successfully installed and even then it will not be flawless. For example, you will no longer be able to make Skype calls directly from Contacts. In order to get this to work, you also have to edit the registry. This can be done with for example Mobile Registry Editor:
http://www.breaksoft.com/Blog/Utilities/20...try_Editor.aspx
HKLMSOFTWARESkypePhoneSkypePath: "PATHNAME"
HKCRcalltoShellOpenCommand: "PATHNAMESkype.exe" %1
Change PATHNAME to the new pathname on the external flash card.
However, it seems that you have some problems with your external flash card, since the installer automatically detects if you have an external flash and gives you the option to install on it if it's present.
What device and flash are you using? Does installation of other applications give you the option to chose to install on external flash?
Any of the following steps might help to get it working. Try installing Skype on external flash for every step.
* Remove the flash card and reinsert it again.
* Soft-reset your device.
* Change HKEY_LOCAL_MACHINESystemStorageManagerPNPWaitIODelay to 1. (Note the old value so that you can reset it if needed)
* Change HKEY_LOCAL_MACHINESystemStorageManagerPNPUnloadDelay to 4096