Login failure when running a SSIS package from a SQL Server job
I had a similar problem while importing data from an Excel file using SSIS packages. I found this tutorial and solved the problem.

EDIT: Important steps: 
1 - When saving the SSIS package to the file system, select the "Package protection level" to "Do not save sensitive data".

Then, follow these steps:
1 - Open the SSIS package in Visual Studio 
2 - Select SSIS -> Package Configurations
3 - On the Package Configurations Organizer click Add
4 - On the window that'll open click Next 
5 - Set the configuration type to XML configuration file
6 - On the Configuration file name click Browse, select the folder in which you want to store the configuration file, choose a name to this file and then hit Save
7 - When you're done here, click Next
8 - Choose the right connection manager and click on the + sign to expand it, then expand Properties and check the checkbox correspondent to Password. Then click Next.
9 - Choose a name to your configuration file and click Finish.

The following XML configuration file will be created on the location you specified previously (here I'm using the code from the tutorial as an example):

&lt;?xml version="1.0"?&gt;

&lt;DTSConfiguration&gt;

      &lt;DTSConfigurationHeading&gt;

            &lt;DTSConfigurationFileInfo GeneratedBy="Domain\UserName" GeneratedFromPackageName="Package" GeneratedFromPackageID="{77FB98FB-E1AF-48D9-8A43-9FD6B1790837}" GeneratedDate="22-12-2009 16:12:59"/&gt;

      &lt;/DTSConfigurationHeading&gt;

      &lt;Configuration ConfiguredType="Property" Path="\Package.Connections[runeet2k8.sa].Properties[Password]" ValueType="String"&gt;

                  &lt;ConfiguredValue&gt;&lt;/ConfiguredValue&gt;

      &lt;/Configuration&gt;

&lt;/DTSConfiguration&gt;


The only thing you'll have to do here is edit the XML file and change this: 
&lt;ConfiguredValue&gt;&lt;/ConfiguredValue&gt;
into this:
&lt;ConfiguredValue&gt;YourPasswordGoesHere&lt;/ConfiguredValue&gt;

Then save the package.

When creating your SQL job, don't forget to add the configuration file to the job in the tab Configurations.