diff --git a/pdf-umbenenner-adapter-out/src/main/java/de/gecheckt/pdf/umbenenner/adapter/out/bootstrap/validation/StartConfigurationValidator.java b/pdf-umbenenner-adapter-out/src/main/java/de/gecheckt/pdf/umbenenner/adapter/out/bootstrap/validation/StartConfigurationValidator.java
index 89ed664..45a8178 100644
--- a/pdf-umbenenner-adapter-out/src/main/java/de/gecheckt/pdf/umbenenner/adapter/out/bootstrap/validation/StartConfigurationValidator.java
+++ b/pdf-umbenenner-adapter-out/src/main/java/de/gecheckt/pdf/umbenenner/adapter/out/bootstrap/validation/StartConfigurationValidator.java
@@ -350,6 +350,12 @@ public class StartConfigurationValidator {
      * This satisfies the "present or technically creatable" requirement: the folder need not
      * exist before the application starts, but must be reachable at startup time.
      * <p>
+     * The write-access check is performed by creating and immediately deleting a temporary
+     * probe file inside the target folder. A pure {@code Files.isWritable} check is not used
+     * because it is known to return false negatives on mapped SMB network drives under
+     * Windows (ACL information as seen by the client can deny writes even when the actual
+     * write succeeds). The probe reflects the real ability to create files in the target.
+     * <p>
      * This separation allows unit tests to inject alternative implementations
      * that control the outcome of write-access or creation checks without relying on actual
      * filesystem permissions (which are platform-dependent).
@@ -368,7 +374,14 @@ public class StartConfigurationValidator {
             if (!Files.isDirectory(path)) {
                 return "- target.folder: path is not a directory: " + path;
             }
-            if (!Files.isWritable(path)) {
+            try {
+                Path probe = Files.createTempFile(path, ".writetest-", ".tmp");
+                try {
+                    Files.deleteIfExists(probe);
+                } catch (IOException cleanupFailure) {
+                    LOG.debug("Could not delete write-probe file {}: {}", probe, cleanupFailure.toString());
+                }
+            } catch (IOException e) {
                 return "- target.folder: directory is not writable: " + path;
             }
             return null;  // All checks passed