Not able to build due to dependencies issue... Failed to read artifact descriptor for org.surfnet.coin:coin-test:jar:2.8.1

[mind-kdas]

I tried to build the project today and am getting the following error..
Primary reason seems to be = >
PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target ->

Could you pls check and let me know how to proceed ....

Thanks in advance..
More error trace below..

[ERROR] Failed to execute goal on project apis-resource-server-library: Could not resolve dependencies for project nl.surfnet.apis:apis-resource-server-library:jar:1.3.6-SNAPSHOT: Failed to collect dependencies at org.surfnet.coin:coin-test:jar:2.8.1: Failed to read artifact descriptor for org.surfnet.coin:coin-test:jar:2.8.1: Could not transfer artifact org.surfnet.coin:coin-test:pom:2.8.1 from/to openconext-releases (https://build.surfconext.nl/repository/public/releases): sun.security.validator.ValidatorException: #######PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target -> [Help 1]######
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal on project apis-resource-server-library: Could not resolve dependencies for project nl.surfnet.apis:apis-resource-server-library:jar:1.3.6-SNAPSHOT: Failed to collect dependencies at org.surfnet.coin:coin-test:jar:2.8.1
at org.apache.maven.lifecycle.internal.LifecycleDependencyResolver.getDependencies(LifecycleDependencyResolver.java:220)
at org.apache.maven.lifecycle.internal.LifecycleDependencyResolver.resolveProjectDependencies(LifecycleDependencyResolver.java:127)