There does not have to be an active task actually running against the CSI. The reason is that a CSI is locked before a task starts running. The tasks that can lock the CSI includes installation, maintenance, configuration or deployment etc.
If you are on one browser session ready to install into an existing CSI, or to apply maintenance, the browser is just sitting there waiting for you to click install, the CSI is already locked at this point even before that task actually starts. IF you then should start another browser session and try another activity on that CSI, You will get the Waiting for SMPE CSI message.
If there is no active task under the Current Tasks tab then there should be a browser session with the base install or maintenance install wizard for the CSI waiting for install to be clicked. This session can be cancelled or the install can be done. After the task completes it will release the CSI.
If the browser session with the base or maintenance install wizard was closed before clicking install or cancel then there is no way to complete the pending task or cancel. In this case the only alternative is to recycle the MSMTC started task.