# Post-Implementation ERP Software Development: Upgrade or Reimplementation
## 5 Discussion  
Maintaining business continuity, and sometimes the risk of system downtime, forces companies to constantly develop and adapt the system to business needs. Changes in technology, customer behaviour, and other business environment factors even exact actions in sustainability. ERP post-implementation phase activities are divided into maintenance classes: corrective, adaptive, perfective, preventive, and user support [39]. External Parties help organizations in implementing this maintenance strategy. ERP upgrades are perfectly suited to the perfective maintenance class; on the other hand, reimplementation activities are impossible to be classified in any class directly. Limiting the budget, avoiding development activities and exclusion of them in obligatory review plans in long-term direct the organization to reimplement the system. It becomes necessary for both technological reasons with the following examples:  
* Inaccessible database service;
* Operating system restrictions;
* Environmental limitations (hardware);
* Limitations related to system integration and its expansion necessity. And business reasons:
* maladjustment to the current requirements of the business environment;
* Up-to-date optimization;
* support for remote work. The analysis shows that years of delays, errors, and negligence in the maintenance phase lead to the necessity of reimplementation instead of upgrading the ERP system. This activities are cross-classes because it is at the same time corrective, adaptive and perfective. Data analysis shows that reimplementation should not be understood as reimplementing the same system. All companies accomplished initial implementation successfully and triggered mainly reimplementation actions because of difficulties with adopting the old ERP version with legal and current user demands. Additionally, time cost and task modifications number were 30% lower than in the initial implementation project. The reimplementation approach, compared to the upgrade approach, is around 50% longer and at least twice as large in modification tasks. Despite the higher costs, two companies decided to go through reimplementation. Analysis shows that it occurred in the case of negligence in the maintenance routine: updates and upgrades. End-user surveys show that, if after initial implementation no upgrades were made after next 2 versions of ERP system, it is required to go through the reimplementation process. The literature analysis shows that many methodologies end the implementation process at the stage of start-up system. Unfortunately, organizations in many cases have finished the development of the ERP system at this stage and limit future activities only to legal adjustment. The consequence of such actions is the necessity to reimplement the system. In the analyzed literature, these activity scopes are rarely undertaken and do not provide standardized implementation methodologies for reimplementation of well-implemented ERP systems. The paper is based on a case study of five past successfully accomplished ERP implementation projects. It should be highlighted that this kind of IT projects was the most consuming IT activity for these companies both in terms of cost and time consumed, mostly for management staff and senior employees. We collected data through observation, study of formal documentation, and interviews with project managers, system integrators, ERP consultants, CIOs. In theory, during the maintenance phase, organizations should follow the following activity classes: areas of corrective, adaptive, perfectible, preventive, and user support. In the business practice, the reality looks differently. The interviews conducted among the analyzed companies show that three of them did not follow through with the upgrade project.