Sometimes Apps on SDcard Not Available As Clickable Icons
Yeah, that's by definition – and the reason why you should never move apps to SD if they provide widgets you want to use.

SDCard gets mounted after the boot_completed broadcast has been sent. So apps installed on the SDCard are not able to receive this broadcast, and thus cannot provide their services "in advance". Depending on how fast your "homescreen" launches, it might already query the widgets before the mount was able to complete – and thus cannot find the apps installed there (which explains the "default icons").

Solution: Move those apps back from the SDCard if you need their widgets.