Sell transaction in investment account fails.

Are there any Placeholder transactions in the account?

About Placeholders (Quicken Windows)

"N/A" in
certain fields of an investment transaction indicates that you have
Placeholder transactions in your account that need to be deleted and replaced
with the correct Buy / Sell / etc. transaction that should have been recorded
here..

For more about Placeholders please go into Quicken Help (press the F1 key from
anywhere in Quicken) and perform a Contents search for
"placeholder".

Alternatively or in addition to the above, read the first few articles found
here: https://www.quicken.com/search/site/placeholder

Also please do this:

Validate

You should validate
your Quicken data file. It may have become damaged over time or if you ever had
crashes, hang-ups or loops while running Quicken. Repeated crashes may
eventually render a data file "broken beyond repair".

Please run this procedure, skipping no steps:

- Make a copy of your data file: Click File / File Operations / Copy.  Do not change any Copy Option settings. Save
file under a new name in same folder as current Quicken data file.  (The Copy process appears to be performing a
record-by-record copy of the data file and not just a simple binary image copy.
This has been reported as recovering some otherwise not repairable
files)

- Open the copied file in Quicken.

- Click File / File Operations / Validate and Repair. Click "Validate
File" and "Rebuild investing lots", check to make sure the
copied file is being validated, click OK. Let it run.

- Fix any errors logged as not repaired by Quicken.

- Now close and restart Quicken using this new file and try your failing action
again. If it works, keep using the new file and abandon the old one.