I think you should use single spaces instead of tabs or multiple spaces in the Bundle-NativeCode
header as the JAR File Specification, Name-Value pairs and Sections specifies:
header: name : value
name: alphanum *headerchar
value: SPACE *otherchar newline *continuation
continuation: SPACE *otherchar newline
Here is a sample manifest.mf snippet which works for me:
Created-By: Apache Maven Bundle Plugin
Bundle-NativeCode: aaaaaaaaaaa.dll, bbbbbbbbbbb.dll, cccccccccc.dll, d
ddddddddddddddd.dll, eeeeeeeeee.dll, ffffffff.dll, ggggggggggggggg.dl
l, hhhhhhhhhhhhhhhhhh.dll, iiiiii.dll