This error indicates that the employee has multiple leave policies, and the leave types are duplicated in both of these policies. The system rule is that each of the policies needs to have a unique leave type. If policy A has a leave type AB, then policy B must not have the same leave type AB. Please do as follows to resolve unable to initialise leave error for your employee:
Go to the Leave Module.
Click on Setup, select Leave Policy and choose the correct leave policy.
Delete the duplicate rows by selecting the ones with the same category and leave type, and click Save.
Go to the Process Leave, click Initialise and select the relevant policy to initialise again.