Hi prajakta
i also faced the same issue.the way to resolve the issue you have to customize the standard task
you have to log in as a administrator download the the task UWL..check the actions in uwl code and remove that one.do with the help of portal consultant.just search Google sample uwl coding with actions compare that code with your downloaded code after enhanced the uwl coding just uplaod with the help of portal consultant.
sample action UWL codings
<ItemType name="uwl.task.webflow.T50012283" connector="WebFlowConnector"
defaultView=“DefaultView" defaultAction=“launchMiniApp" >
<ItemTypeCriteria externalType="T50012283"
connector="WebFlowConnector"/>
<Actions>
<Action name="launchMiniApp" handler="SAPMiniAppLauncher">
<Properties>
<Property name="Template" value="BWWF_WI_DECI"/>
</Properties>
<Descriptions default="">
<ShortDescriptions/>
</Descriptions>
</Action>
</Actions>
</ItemType>
Regards
Jayaprakash T