Error running build with Milestone-5 using SYSTEM account

My buildfile adds JAR deps to Gradle’s classpath (using Saxon classes directly to compile XSLT files). This worked in MS-3 but stopped working in MS-5 when running under SYSTEM-account on Windows (CI-Server). Running the same script under “normal” user account does work. Are there any known problems or steps to debug this issue? Thanks.

Update: it seems the issue is that the unresolved dependency was downloaded as a 0-byte JAR, which is clearly an error that should be caught by Gradle (whatever caused this broken download/storing of artifact).