To create a watch only address, you use the public key. But if you want to use an address, you create it from a private key. Did you sent the ltc to an address where you created with "Master Public Keys"? If so, then you don't have access to the address.
The other times you sweeped coins, you must have sent it to a pregenerated address.
Honeslty I couldnt understand well what you are saying. This address is watch only but I see that 20 days ago I used to sweeped in or transfered coins out of this address to my main address. Unfortunately I dont remember how did I do that or how did I create this watch only address. I just have some random numbers saved under the title of _etm_template_uuid. Do you think this might have enabled the transfer before? Any help would be great pls.