If you run into the problem described in:

2639184    SharePoint 2010: DataForm Web Part displays "Unable to display this Web Part"

we might have another solution for you.

Our KB article 2597136 contains the following line that describes the issue but needs some more steps after you have installed the hotfix.

When you try to open a large .xsl file by using a Data Form Web Part (DFWP) on a SharePoint Foundation site, the DFWP does not display the file.

We highly recommend to use the following steps to change the behavior:
Install February 2012 cumulative update (Full Server package) for Microsoft SharePoint Foundation 2010 or SharePoint Server 2010

The code change is in the Microsoft.SharePoint.DLL with build 14.0.6117.5002 and later also on higher builds as usual.

Now you need to test which value might be a better one than One Second timeout.

On SharePoint Server log in with your Farm Account.
Start PowerShell in an elevated mode; check http://blogs.msdn.com/b/joerg_sinemus/archive/2010/08/16/what-is-the-difference-between-local-administrator-and-machine-administrator.aspx for more information.

The following code lines will set the timeout to five seconds:

$farm = Get-SPFarm
$farm.XsltTransformTimeOut = 5

In a discussion forum I read that two seconds are also a good value but everything depends as usual on the overall performance on the server side.