Salesforce has limitations on the number of custom fields allowed on an object. It is important to note that fields from managed package do not count against these limits for any custom or standard object except Activity Object. For Activity object, the limits are different compared to any other object and mainly managed fields also count against this limit.

You must review the number of custom fields in the org before upgrading ServiceMax package version, otherwise the package installation may fail. This is true for Activity Object where managed fields are counted towards the limit.

When you install SVMX package/app on a new org that does not have any customizations, the number of fields on Activity object looks as the following:

The following screen displays the Object limits - Activity in Upgrade Considerations.