If QA_DEBUG_PERFORMANCE in qa-config.php is set to true, errors will occur in some plugins. In my case, error is shown on plugin option setting. This seems to be due to strange lines added in V1.8.1.
For example: qa-include/qa-app-updates.php
if (defined('QA_DEBUG_PERFORMANCE') && QA_DEBUG_PERFORMANCE) {
trigger_error('Included file ' . basename(FILE) . ' is deprecated');
}
Does this happen at your site?