Apple recently released OS X 10.9.4, which addresses several problems with Macs being unable to connect to Wi-Fi networks, and improving the system’s ability to wake from sleep without pauses or other problems. The update is available through the App Store, but when some people have attempted installing it, they have run into an “invalid checksum” error that prevents them from applying the update.

This problem happens even when the update is re-downloaded, and does not clear when performing steps like restarting in Safe Mode and fixing permissions. In addition, the problem may persist through the use of standalone updaters, which Apple makes available in addition to the App Store download.

If you encounter this problem, there are several things you can try. First, if you have not already done so, then try downloading the 10.9.4 Combo updater from Apple and run this manually by opening the downloaded disk image, and then running the installation package it contains.

If this still shows the same problem, then go to the following directory on your computer (you can highlight the entire line, right-click it, and choose the option to reveal or open it from the Services submenu):

/Library/Updates

With the updates folder opened, locate the downloaded updater file, which should be named accordingly, and remove it. It is ok to remove all items from this folder; however, for starters simply remove the relevant update and try again. If the problem still occurs, then go ahead and remove all items from this folder and try again.

If you have manually downloaded the OS X update from Apple’s Web site and are encountering checksum errors, then be sure to check the update against the checksum that Apple includes on the update page. For example, the checksum for the recent OS X 10.9.4 combo update is “3c02ee0c3e2aa11831547571dd6fa502130ee5d6,” and you can check this for the downloaded disk image by opening the Terminal utility and typing “shasum” followed by a single space. Then drag the disk image to the Terminal window to enter the full path to the image, followed by pressing Enter to calculate the SHA1 checksum.

If the string of output characters do not match the checksum on Apple’s Web site, then the file is different from the one Apple intended to publish, and you should delete it and re-download the update. Note that perhaps the issue is a small alteration or other error on Apple’s end, so you might consider waiting a day or two for the situation to be found and fixed, before trying again.