Problem in saving the workflow

Last two days i have been facing this problm where I am unable to save my workflows.

Error Message:-
FATAL InplaceSaveRunnable File not found - this exception will be re-thrown as an InterruptedException.
ERROR WorkflowEditor Could not save + workflow: File access problems: L:\KNIME_project\File Reader (#2)\port_1\ (Access is denied)

Please help me out.
Thank you

Duplicate: error with Excel Sheet Appender (XLS)