It sounds to me like your price history is corrupted.
You can try this:
- click Investing (Quicken menu row)
- put your cursor on Investing Tools and select Security Detail View
- choose a problem security in the security dropdown
- click Update (in the Security Detail View menu row) and select Edit Price History
- check the resulting list of historical security prices to see if any look fishy (most likely the price with the most recent date)
- if you find any invalid dates/prices, delete them
- click "New" in the Edit Price History menu row and try to add the price you could not add using the Portfolio
- if that succeeds, repeat for the other problem securities
If you're still unable to add a valid price, post back for further instructions.