"You have reached the maximum allowance of 100 location records. To create additional locations, an administrator must enable the Advanced Item Location Configuration feature" - Message.

If Multi-Location Inventory (MLI) feature is enabled, users may have up to a maximum of 100 location records only. The said number of locations include those that were created prior to enabling MLI.  The 100 Location Limit only applies to ACTIVE location records. Thus, INACTIVE Locations do NOT count against the total Location limit.

Users may opt to inactivate the other location records that are no longer used in order to create new location records in the system.

Solution

If there is a valid need to increase this limit and existing locations cannot be set as inactive,

Enable Advanced Item Location Configuration feature. 

a. Navigate to Setup> Company > Enable Features > Items & Inventory tab.

b. Mark the checkbox for Advanced Item Location Configuration feature.

c. Save.

NOTE

Once this feature is enabled and there are 100+ active locations set, it cannot be disabled.

Enabling the said feature will allow the user to create more than 100 locations.  No limit has been set yet on the number of locations that can be created.   Performance will improve as users may filter data display in item records based on location attributes.

However, This feature will restrict users from updating Item Location Attribute fields of item records via Web Services.