I have had my site up with an edited version of default theme for a few days and it has been working very well. Suddenly today when I tried to change album titles and description, as soon as I click on "apply" all the fields become blank and titles and descriptions are erased. When I click on the "images" tab under albums in admin.php, as soon as I click "apply" the green "changes applied" banner appears at the top but all image titles and descriptions are suddenly erased.

Am I missing anything obvious?

That is of course nothing that should happen. As always you will need to look at the server error log to see if there anything is noted. It might always happen that the host updates something that causes sideeffects (mine recently updated their security setting which made my whole webspace inaccessible accidentally).

Nothing in the server error log... I contacted the host and they said that they haven't updated anything in the last month. I guess I should just try to erase and reinstall zp... It's just weird that it was working fine and then suddenly wasn't.

Actually... I just found this in my zp debug report... But I don't think I made any changes to functions-basic.php

Could this be the cause of admin.php behaving this way?

{Tue, 17 Jul 2012 06:00:57 GMT} Zenphoto v1.4.3[10393]

Backtrace: WARNING: htmlspecialchars() [function.htmlspecialchars]: Invalid multibyte sequence in argument in /home/jrm/public_html/Gallery/zp-core/functions-basic.php on line 260

htmlspecialchars called

from html_encode (functions-basic.php [260])

from printPageListWithNav (template-functions.php [814])

from include (index.php [105])

from index.php [92]

{Tue, 17 Jul 2012 06:00:57 GMT}

Backtrace: WARNING: htmlspecialchars() [function.htmlspecialchars]: Invalid multibyte sequence in argument in /home/jrm/public_html/Gallery/zp-core/functions-basic.php on line 260

htmlspecialchars called

from html_encode (functions-basic.php [260])

from printPageListWithNav (template-functions.php [912])

from include (index.php [105])

from index.php [92]

{Tue, 17 Jul 2012 06:05:14 GMT}

Backtrace: WARNING: htmlspecialchars() [function.htmlspecialchars]: Invalid multibyte sequence in argument in /home/jrm/public_html/Gallery/zp-core/functions-basic.php on line 260

htmlspecialchars called

from html_encode (functions-basic.php [260])

from printPageListWithNav (template-functions.php [814])

from include (index.php [105])

from index.php [92]

{Tue, 17 Jul 2012 06:05:14 GMT}

Backtrace: WARNING: htmlspecialchars() [function.htmlspecialchars]: Invalid multibyte sequence in argument in /home/jrm/public_html/Gallery/zp-core/functions-basic.php on line 260

htmlspecialchars called

from html_encode (functions-basic.php [260])

from printPageListWithNav (template-functions.php [915])

from include (index.php [105])

from index.php [92]

Which theme is that? What does the function call in the theme page look like?

I have a similar challenge: I use version 1.4.3 [10458] (Official build). If I make a copy of the Stopdesign theme and then try two change the theme options, it does not work, i.e., I cannot change the number of thumbs per page and alike - editing is simply not possible. Tried it with Safari as well as with Chrome.

Probably you cannot change those options on the distributed version of the theme either. Stopdesign does not allow changing those items.