A customer reported this problem while sending requests from his user-written client to AP Web Services. After solving the problem, I wrote the following knowledge document that provides more detail about what could cause this error message and what to check in order to troubleshoot and solve the problem:
http://www.ca.com/us/support/ca-support-online/product-content/knowledgebase-articles/tec1154531.aspx
Automation Point support understands that other customers may be affected by this same issue when using AP Web Services, and we hope this KD provides repeat value. Feel free to ask any questions you might have about AP Web Services, and I'll be happy to provide the support you need to get maximum value using this component of the product.