Why am I seeing strange errors after upgrading?

Make sure all of the files were updated, in particular pmwiki.php.

This question sometimes arises when an administrator hasn't followed the advice, which used to be less prominent, on the installation and initial setup tasks pages and has renamed pmwiki.php instead of creating an index.php wrapper script. If you have renamed pmwiki.php to index.php, then the upgrade procedure won't have updated your index.php file. Delete the old version and create a wrapper script so it won't happen again.

Sometimes an FTP or other copy program will fail to transfer all of the files properly. One way to check for this is by comparing file sizes.

Be sure all of the files in the wikilib.d/ directory were also upgraded. Sometimes it's a good idea to simply delete the wikilib.d/ directory before upgrading. (Local copies of pages are stored in wiki.d/ and not wikilib.d/.)

I'm suddenly getting messages like "Warning: fopen(wiki.d/.flock): failed to open stream: Permission denied..." and Cannot acquire lockfile"... what's wrong?

Something (or someone) has changed the permissions on the wiki.d/.flock file or the wiki.d/ directory such that the webserver is no longer able to write the lockfile. The normal solution is to simply delete the .flock file from the wiki.d/ directory -- PmWiki will then create a new one. Also be sure to check the permissions on the wiki.d/ directory itself. (One can easily check and modify permissions of the wiki.d/ directory in Filezilla (open-source FTP app) by right-clicking on the file > File attributes)

My links in the sidebar seem to be pointing to non-existent pages, even though I know I created the pages. Where are the pages?

Links in the sidebar normally need to be qualified by a WikiGroup in order to work properly. Otherwise they will point to whatever group you happen to be viewing the sidebar in.
Also: Make sure you type SideBar with a capital B.

Why am I seeing "Warning: Cannot modify header information - headers already sent ..." messages at the top of my page.

If this is the first or only error message you're seeing, it's usually an indication that there are blank lines or spaces before the <?php or after the ?> in a local customization file. Double-check the file and make sure there aren't any blank lines or spaces before the initial <?php. It's often easiest and safest to eliminate any closing ?> altogether.

If the warning is appearing after some other warning or error message, then resolve the other error and this warning may go away.

Why is PmWiki prompting me multiple times for a password I've already entered?

Usually this is an indication that the browser isn't accepting cookies, or that PHP's session handling functions on the server aren't properly configured. If the browser is accepting cookies, then try setting $EnableDiag=1; in local/config.php, run PmWiki using ?action=phpinfo, and verify that sessions are enabled and that the session.save_path has a reasonable value. Note that several versions of PHP under Windows require that a session_save_path be explicitly set (this can be done in the local/config.php file).

I edited config.php, but when I look at my wiki pages, all I see is "Parse error: parse error, unexpected T_VARIABLE in somefile on line number."

You've made a mistake in writing the PHP that goes into the config.php file. The most common mistake that causes the T_VARIABLE error is forgetting the semi-colon (;) at the end of a line that you added. The line number and file named are where you should look for the mistake.

Searches and pagelists stopped working after I upgraded -- no errors are reported, but links to other pages do not appear (or do not appear as they should) -- what gives?

Be sure all of the files in the wikilib.d/ directory were also upgraded. In particular, it sounds as if the Site.PageListTemplates page is either missing (if no links are displayed) or is an old version (if the links do not appear as they should).

Some of my posts are coming back with "403 Forbidden" errors or "Not Acceptable"? This happens with posts containing "wget", "curl", "file(" or ...

Your webserver probably has mod_security enabled. The mod_security "feature" scans all incoming posts for forbidden words or phrases that might indicate someone is trying to hack the system, and if any of them are present then Apache returns the 403 Forbidden error. Common phrases that tend to trigger mod_security include "curl ", "wget", and "file(", although there are many others.

Since mod_security intercepts the requests and sends the "forbidden" message before PmWiki ever gets a chance to run, it's not a bug in PmWiki, and there's little that PmWiki can do about it. Instead, one has to alter the webserver configuration to disable mod_security or reconfigure it to allow whatever word it is forbidding. Some sites may be able to disable mod_security by placing SecFilterEngine off in a .htaccess file.

I get the following message when attempting to upload an image, what do I do?

Warning: move_uploaded_file(): SAFE MODE Restriction in effect. The script whose uid is 1929 is not allowed to access /home/onscolre/public_html/pmwikiuploads/Photos owned by uid 33 in /home/onscolre/public_html/pmwiki/scripts/upload.php on line 198

PmWiki can't process your request

?cannot move uploaded file to /home/onscolre/public_html/pmwikiuploads/Photos/FoundationPupilsIn1958.jpeg

We are sorry for any inconvenience.