Failed Action: Upload

I'm getting the following error after a .NET install to .NET 4.5 (RTM). I've not changed the application to .NET 4.5 just installed the .NET 4.5 package.

This is related to Ajax upload, and I get it every time I'm trying to upload a PDF.

Failed Action: 
    Upload
Path: 
    MusicPartnerWeb Filer\FunkyKidz
Parameters: 
    State: GleamTech.Web.UI.FileManagerState
    InstanceID: f9efb345cdcd0a1c9f68
    RootFolderIndex: 0
    Path: FunkyKidz
    RootFolder: GleamTech.Web.UI.FileManagerRootFolder
Error: 
    System.IO.InvalidDataException: Multipart boundary not found.
   at A.cdd3165295593a4eafbb538f58cf015b1.cf3c9f1b48d90b2b7a62bab0d2f7ae773()
   at GleamTech.Web.UploadModule.c935bcf50e95065f050ff5110451bb643(HttpContext cb13035873f180013b7025a364931d0f6)

/K1