There's been a problem, it's almost certainly the signature form. At the moment the sig submitted MUST be a valid Tika Signature XML doc, including an XML prolog.
Below is a PDF example
<xml version="1.0" encoding="UTF-8"?> <mime-type> <magic priority="50"> <!-- ASCII: %PDF-1. @0 --> <match value="0x255044462D312E" type="string" offset="0"> <!-- ASCII: % @9 --> <match value="0x25" type="string" offset="9"> </match> </match> </magic> <glob pattern="*.pdf"/> </mime-type> <#else> ${result.hash64K} ${result.mime} ${result.duration} milliseconds #if>