In a few cases, we've seen that this can be due to some PHP settings causing the demo install to timeout. Below are listed the three settings that could be the cause.
- max_execution_time
- memory_limit
- post_max_size
Temporarily increasing the 'max_execution_time' to be 60 seconds or higher and the 'memory_limit' and 'post_max_size' to be 64MB or larger should resolve this issue.
These options can usually be set from your hosting control panel or through the 'php.ini' file, although some hosts might prevent you from manually editing these values in which case you would need to contact your hosting provider to make the change.