I did find this error on a Windows Server 2008 and SQL Server 2008 installation but as you will see the error is not tied to an specific SQL Server or Windows version.

In this case my customer was trying to run a SQL Server Agent Job with 17 different steps. These steps were of different types like running T-SQL code, ActiveX scripts, Operating System (CmdExec), etc. The customer was looking to run all these job steps using a Proxy account, which is a way to restrict the security context where a job step is run in SQL Server; here you can read the Proxy Account definition from MSND:

SQL Server Agent lets the database administrator run each job step in a security context that has only the permissions required to perform that job step, which is determined by a SQL Server Agent proxy. To set the permissions for a particular job step, you create a proxy that has the required permissions and then assign that proxy to the job step. A proxy can be specified for more than one job step. For job steps that require the same permissions, you use the same proxy.

When using the Proxy account, two different jobs steps were failing with the following error:

The error when running SSIS-step (11,12) using a proxy is:
10.0.2531.0 for 64-bit  Copyright (C) Microsoft Corp 1984-2005. All rights reserved.    Started:  15:27:31  Error: 2010-10-16 15:27:32.38     Code: 0xC020200E     Source: Copy Data from AgentSource to AgentDestination Task Flat File Source [1]     Description: Cannot open the datafile "V:\MySharedFolder\MyTextFile.txt".  End Error  Error: 2010-10-16 15:27:32.38     Code: 0xC004701A     Source: Copy Data from AgentSource to AgentDestination Task SSIS.Pipeline     Description: component "Flat File Source" (1) failed the pre-execute phase and returned error code 0xC020200E.  End Error  DTExec: The package execution returned DTSER_FAILURE (1).  Started:  15:27:31  Finished: 15:27:32  Elapsed:  0.687 seconds.  The package execution failed.  The step failed.

In this case the job owner was the ‘sa’ account so we first tried to avoid the error by changing the job owner from ‘sa’ to the Proxy account but this did not fixed the problem. During the troubleshooting process I worked using a remote session with the customer’s server to try to determine where the error was coming from; during that session I noticed that the V: drive the job was pointing to did not exist on the server. The customer explained to me that the drive mapping was taking place during the first job step.

The mapping of the V: drive was taking place on the security context of the Proxy account so we first check for the correct xp_cmdshell permission for this account, as described in this MSND entry:

When it is called by a user that is not a member of the sysadmin fixed server role, xp_cmdshell connects to Windows by using the account name and password stored in the credential named ##xp_cmdshell_proxy_account##. If this proxy credential does not exist, xp_cmdshell will fail.
The proxy account credential can be created by executing sp_xp_cmdshell_proxy_account. As arguments, this stored procedure takes a Windows user name and password. For example, the following command creates a proxy credential for Windows domain user SHIPPING\KobeR that has the Windows password sdfh%dkc93vcMt0.

EXEC sp_xp_cmdshell_proxy_account 'SHIPPING\KobeR','sdfh%dkc93vcMt0'

In our case the permissions required by the Proxy account were correctly assigned so we tried to map the network drive out of the job execution, using our own session instead of the Proxy account session, but the result and error was exactly the same. Nevertheless, both the customer and myself kept thinking that the problem was related to the mapping of this drive so we created a new Agent job with the following single step to isolate the problem (abridged):

net use v: \\server\share\ /user:username /persistent:yes
c:\program files (…) dtexec.exe package.dtsx (…)
dir v:\*.* > c:\out.txt

This test worked. The difference here was that we were mapping and running the package in the same job step while the customer was mapping the drive in the first step, and executing the SSIS tasks in the subsequent job steps. As explained in KB180362 article this was precisely the problem with the Agent job:

When the system establishes a redirected drive, it is stored on a per-user basis. Only the user himself can manipulate the redirected drive. The system keeps track of redirected drives based on the user's Logon Security Identifier (SID). The Logon SID is a unique identifier for the user's Logon Session. A single user can have multiple, simultaneous logon sessions on the system.

If a service is configured to run under a user account, the system will always create a new logon session for the user and then launch the service in that new logon session. Thus, the service cannot manipulate the drive mappings that are established within the user's other session(s).

At the beginning of the same KB article you can also read:

A service (or any process that is running in a different security context) that must access a remote resource should use the Universal Naming Convention (UNC) name to access the resource. UNC names do not suffer from the limitations described in this article.

In our case the solution was as easy as replacing the mapping to the V: drive for the UNC path (i.e. \\servername\sharename). Another option in this scenario is to perform the mapping on the same job step as the one where the action takes place.