Thread:Project:Support desk/no content in pages/reply

See Manual:Errors and symptoms. It's caused by a PCRE upgrade.

This error is fixed in latest 1.22 releases, but apparently it hasn't been backported to 1.19 and 1.21 yet. You coould apply the patch for your version until a new release is made which would include this fix. You can look for the patch for your version here: