I deactivated the WWSGD plugin and that error line went away. Other still persists.
It will hold a text widget if it is only text. I try to add a link or image, the whole text widget disappears. It not only disappears from my sidebar on my site but also when I go back into edit widgets at the dashboard. Gone. Not even a blank text widget left behind.
You have serious code errors that may be having cascading effects. If the code that you are entering in the text widget has errors, then it may not appear or cause other display problems.