This frequently appears on the Income Tax portal if your PAN was not generated via the "Instant e-PAN" facility.

If your Aadhaar is not linked to an active mobile number, you cannot receive the mandatory OTP for authentication.

Many users think they can’t download or open the file, but they are actually using the wrong password. The standard password is your Date of Birth in DDMMYYYY format (e.g., 01011990). 2. How to Download Based on Your Portal