This happens because you have executed version 1.8.8-1 after running version 1.8.8-2. This should not happen under normal conditions.
To fix this issue, do the following:
- From the main menu, select Resources > Updates > Manage Repositories.
- On the Manage Update Repositories dialog, click Default, then OK.
This will reset update repositories to the default ones required by the running PixInsight application.