You might want to read this KB article if you're using an Agent running on Windows (as indicated by the fact that you're using file explorer).
Please also check that the the user running the agent has full control over the file and parent folder.
This normally works better when done explicitly on the user permission rather than on group permission.
Before configuring the connection, confirm that all the permissions from the current drive are enabled on the mapped drive.
In Informatica Cloud Service, to configure a Flat File connection on a mapped drive, do the following:
- Ensure that the agent is running with a local user account and not the system account.
- Run the command net use x: <drive to me mapped> /persistent:yes.
- Map the drive using a free alphabet.
- Provide the full path name in the Flat File connection.