HTTP Client POST Service : General Engine Error - "INVALID_CHARACTER_ERR: An invalid or illegal XML character is specified"

Symptom

Business process is going in "halted" status with error "General Engine Error" at step HTTP Client POST Service

In httpclient.log in debug modus, following error is raised :

[2016-02-15 16:15:42.426] DEBUG <-227305982>
HttpClientAdapter.fillProcessData() - adding header name
[Content-Length] with value [520]
[2016-02-15 16:15:42.426] DEBUG <-227305982>
HttpClientAdapter.fillProcessData() - adding header name [Date] with
value [Mon, 15 Feb 2016 15:15:41 GMT]
[2016-02-15 16:15:42.426] DEBUG <-227305982>
HttpClientAdapter.fillProcessData() - adding header name [Content-Type]
with value [text/xml; charset=utf-8]
[2016-02-15 16:15:42.426] DEBUG <-227305982>
HttpClientAdapter.fillProcessData() - adding header name [Server] with
value [Microsoft-IIS/8.5]
[2016-02-15 16:15:42.426] DEBUG <-227305982>
HttpClientAdapter.fillProcessData() - adding header name [Cache-Control]
with value [private]
[2016-02-15 16:15:42.426] DEBUG <-227305982>
HttpClientAdapter.fillProcessData() - adding header name
[X-AspNet-Version] with value [4.0.30319]
[2016-02-15 16:15:42.426] DEBUG <-227305982>
HttpClientAdapter.fillProcessData() - adding header name
[X-Content-Type-Options] with value [nosniff]
[2016-02-15 16:15:42.426] DEBUG <-227305982>
HttpClientAdapter.fillProcessData() - adding header name
[X-XSS-Protection] with value [1; mode=block]
[2016-02-15 16:15:42.426] DEBUG <-227305982>
HttpClientAdapter.fillProcessData() - adding header name [X-Served-By]
with value [4]
[2016-02-15 16:15:42.426] DEBUG <-227305982>
HttpClientAdapter.fillProcessData() - adding header name [*] with value
[*]
[2016-02-15 16:15:42.426] ERROR <HAR.100094313.Thread>
HTTPClientPostService.primitiveProcessData() - General Exception:
INVALID_CHARACTER_ERR: INVALID_CHARACTER_ERR: An invalid or illegal XML character is specified.
[2016-02-15 16:15:42.426] ERROR <HAR.100094313.Thread> [1455549342426]
INVALID_CHARACTER_ERR: Un caractère XML non valide ou incorrect est
indiqué.
[2016-02-15 16:15:42.426] ERRORDTL <HAR.100094313.Thread>
[1455549342426]org.w3c.dom.DOMException: INVALID_CHARACTER_ERR: An invalid or illegal XML character is specified.
at org.apache.xerces.dom.CoreDocumentImpl.createElement(Unknown
Source)
at
com.sterlingcommerce.woodstock.xpathutil.XPathHelper.createNode(XPathHel
per.java:1467)
at
com.sterlingcommerce.woodstock.xpathutil.XPathHelper.createTargetContext
(XPathHelper.java:1141)
at
com.sterlingcommerce.woodstock.xpathutil.XPathHelper.createTargetContext
(XPathHelper.java:1053)
at
com.sterlingcommerce.woodstock.workflow.WFCUtil.setDataInTree(WFCUtil.ja
va:1113)
at
com.sterlingcommerce.woodstock.workflow.WFCUtil.setDataInTree(WFCUtil.ja
va:784)