If you are writing manifests which include using templates and you receive a wrong header line format error message, it means there is a syntax error in one of your template files. The message is pretty much worthless due to it’s cryptic nature, and there appears to be an open defect to improve the messaging, but not sure that it will be fixed as the current status is “accepted”.

So check your templates, the issue that generated this warning for me was:

# Notice the <% = 
# Should be <%=
alias /<%= tpl_src_code_path %>/<% = static_asset_dir %>/;