I started to run into this error in the last month or so. I’ve been developing SSIS 2005 packages on my desktop which is an XP Professional and deploying them to Windows Server 2003 R2 Enterprise x64 edition. All was well until recently, according to Microsoft one of the updates broke compatibility on a dll and caused this issue (More details here in the Microsoft KB 931846). There were a few suggestions such as open the packages on the target server and make an update and save them to force recompile. This is not fun when you have multiple packages and in some instances did not do the trick.
My solution which has worked consistently so far is to restart the Integration Services after you deploy the updated packages on the target server.