I've not encountered such a problem before so, unfortunately, I do not know what might be causing it.
However, here are a few things to check and try which might help.
(1) Change your password
Try changing your Showkase login password by following the procedure noted in the FAQ below.
I lost my password, how can I reset it?
(2) Upgrade (or reinstall) Showkase
If you are not already using the latest version of Showkase (v1.7.3), then try upgrading following the Upgrading Showkase instructions.
Even if you are already using the latest version, try reinstalling it to ensure that all core Showkase files are present and correct on your web server.
(3) Run the Showkase Server Compatibility Test
Try running the Showkase Server Compatibility Test.
Even if you ran the test before initially installing Showkase, please try again in case your web host has made any changes recently and any of the tests currently fail.
The results of the tests may point us in the right direction.
There are troubleshooting tips for any test fails that you may encounter on the test's support page.
(4) Run Showkase in debug mode
Try running Showkase in debug mode to see if any error messages or warnings are displayed in the application's status bar which might help to pinpoint the cause of the problem.
Open your 'showkase/admin/settings/constants.php' file in a plain text editor and change line 12 from:
Please note that the line number above refers to the current version of Showkase (v1.7.3).
(5) Check in with your web host
If the problem has only started to happen recently and you have not changed anything yourself, then this suggests that something might have changed on your web server.
Please ask your web host to see if they have made any changes recently which might be affecting your hosting account (and, subsequently, Showkase's functionality).
I hope these suggestions help.
Please let me know how you get on and if I can be of any further assistance.