The extension xla denotes an Open XML Macro-enabled AddIn for Microsoft Excel. The XLAM files include VBA (Visual Basic for Applications) and may contain macro code. They can be loaded when starting Excel.
AddIns extend Excel with additional features, such as new features or the ability to run macros. These add-ins can be created by the user or come from other developers.
The Open XLM format has been used by Excel since 2007 (Mac 2008). It is based, as the name suggests, on XML and is compressed using the Zip algorithm. For the 2000, 2003, and XP Office versions, this functionality can be remedied using the Microsoft Office Compatibility Pack, which may limit the use of XLAM files.
Excel AddIns can be managed and loaded in the options under AddIns.
Most often resolving problems with opening XLAM files is very simple. Just install an appropriate program that supports such files. All of the listed programs support XLAM files, but may vary in offered function and purpose. Some programs may be capable only of viewing contents of XLAM files or offer file conversion options, but may not be capable of editing such files.
It is possible that although a compatible program has been installed on user’s system, it is not used by the system to open it. This may happen because no default application was associated with this type of files. To associate XLAM files with given application, select "Open with" from drop-down menu (accessed by right-clicking on the file). Then select from the list the program or application you want to be used to open this type of file. If the Microsoft Excel applications is not on the list, select "Browse" option in order to manually locate the directory where Microsoft Excel has been installed.
Sometimes problems with opening XLAM files may not lie with the application itself, but can arise due to other causes, such as: