I had the same problem with another mutual fund. The 'Edit Portfolio' screen has a bug that should be fixable. It is possible to get the screen to work but you need to jump through some hoops when it does happen.
Most people probably never used the 'Edit Portfolio' screen because it's only used to change the default currency, change the portfolio sort order or to enable/disable dividend reporting. Furthermore, you will not run into the "Symbol(s) invalid or unsupported: " problem if you don't actually change anything.
There is a work around that is suggested at in earlier post from Karolina but is not explained. In last post from "J J Hanlon", they need to change TRVLX to MUTF:TRVLX in the text box when they click "Save Changes" on this page. They will also need to prepend the symbol + ':' to the correct exchange for every other symbol in the list (assuming something on the page has changed).
If you need to change a different symbol, you should go to
www.google.com/finance and search for your symbol. If it finds your symbol you will see symbol <tab> symbolDescription <tab> exchange. Examples...
Symbol Description Exchange
T AT&T NYSE
TRVLX T. Rowe Price Value Fund MUTF
GOOG Google Inc NASDAQ
You will need to find the exchange (the rightmost text) and prepend the symbol with the exchange + ":". For T change T to NYSE:T. For TRVLX change to MUTF:TRVLX.
Every time you use the "Edit Portfolio" screen (and you actually change something on the page) you have to change all symbols by adding its exchange + ":" in front of the symbol.
**** Notes to Google developers (Assuming that this is not just a forgotten 20% project that nobody cares about) ***
1) I'm going to give you the benefit of the doubt here. I'm hoping that you are using some type of unit testing software. Change your tests to actually change a value on the screen before invoking the "Save Changes". This only fails if something is different. Easily overlooked.
2) I'm assuming all your assets are in Google stock. Diversify! Get some mutual funds that don't own google and you might have found this problem on your own. :).