The designed behavior in SSIS is to prevent storing passwords in a package, because it's bad practice/not safe to do so.
Instead, either use Windows auth, so you don't store secrets in packages or config files, or, if that's really impossible in your environment (maybe you have no Windows domain, for example) then you have to use a workaround as described in http://support.microsoft.com/kb/918760 .The simplest answer is a config file to go with the package, but then you have to worry that the config file is stored securely so someone can't just read it and take the credentials.
in addition you can find this 5 methods:
Method 1: Use a SQL Server Agent proxy account Create a SQL Server Agent proxy account. This proxy account must use a credential that lets SQL Server Agent run the job as the account that created the package or as an account that has the required permissions.
This method works to decrypt secrets and satisfies the key requirements by user. However, this method may have limited success because the SSIS package user keys involve the current user and the current computer. Therefore, if you move the package to another computer, this method may still fail, even if the job step uses the correct proxy account. Back to the top
Method 2: Set the SSIS Package ProtectionLevel property to ServerStorage Change the SSIS Package ProtectionLevel property to ServerStorage. This setting stores the package in a SQL Server database and allows access control through SQL Server database roles. Back to the top
Method 3: Set the SSIS Package ProtectionLevel property to EncryptSensitiveWithPassword Change the SSIS Package ProtectionLevel property to EncryptSensitiveWithPassword. This setting uses a password for encryption. You can then modify the SQL Server Agent job step command line to include this password.
Method 4: Use SSIS Package configuration files Use SSIS Package configuration files to store sensitive information, and then store these configuration files in a secured folder. You can then change the ProtectionLevel property to DontSaveSensitive so that the package is not encrypted and does not try to save secrets to the package. When you run the SSIS package, the required information is loaded from the configuration file. Make sure that the configuration files are adequately protected if they contain sensitive information.
Method 5: Create a package template For a long-term resolution, create a package template that uses a protection level that differs from the default setting. This problem will not occur in future packages.