What is the MOST likely cause of application access issues if a server has not rebooted in a long time?

The most likely cause of application access issues on a server that has not been rebooted in a long time is a memory leak. Over time, applications can consume more memory than they release back to the system. This situation occurs when a program allocates memory for its needs but fails to release it when it is no longer required. As these leaks accumulate, they can exhaust the available memory on the server, leading to performance degradation and ultimately causing issues with application access.

When a server runs out of memory, it might start killing processes or applications to free up resources, which can lead to applications becoming unresponsive or inaccessible. Regularly rebooting the server can help clear these leaks, allowing the system to reclaim the memory and restore application functionality.

In contrast, low resources or slow OS performance might contribute to access issues but are less directly tied to the longstanding uptime without a reboot. Service failure could cause specific applications to become unavailable but is often easier to diagnose and resolve than issues stemming from a memory leak.