Have you tried downloading vbgallery 3.02 and in your product mananger in vb reimport ther product-ppvbgallery42.xml selecting the overwrite option.
Your using a version of vbgallery that is not compatible with vb 4.20
You say your running vbGallery 3.01 on vb 4.1.11 which works fine. However your using vbulletin 4.2
That would be my guess hard to say since you appear to have removed your vbullletin branding.