Whether you're a developer maintaining legacy systems or a user just trying to launch an old favorite program, here is everything you need to know about this version. What is .NET Framework 4.0.3019?

"This application requires .NET Framework version 4.0.3019. Please contact your vendor."

The version number specifically refers to the .NET Framework 4 Platform Update 1 (KB2478063) , often associated with the Multi-Targeting Pack .

If you are encountering this version number today, it is likely due to one of three scenarios:

None of this made headlines. But for developers running high-frequency trading platforms, hospital lab systems, or airport baggage scanners, was the version that stopped the 3 a.m. pages.