Library no longer working with updated API

[ghost]

I'm getting this error message when try to retrieve contact with parameters ContactID:
<xmp>

0
Operator '==' incompatible with operand types 'Guid' and 'String'

</xmp>
and when retrieve contact by using other parameters ("Name" etc), no information is returned:
<xmp>

6c5fbf40-0af2-4326-97eb-b384693f1e3b
OK
SXI-SHOPP XERO Private Integrator
2010-08-14T09:13:05.7253215Z

</xmp>
It was working before and this suddenly happened!

[ghost]

And when put a new contact, invoice or payment, I get this message back:
An error occurred in Xero please contact [email protected]. (ErrorNumber 500)
Put the same input xml works correctly with API Previewer in api.xero.com