The most reliable follow-up procedure to determine if management has resolved the finding of non-sequential purchase order numbers is to inspect the system settings and transaction logs to determine if sequential order numbers are generated. This will provide direct evidence of the system's functionality and compliance with the audit recommendation. The other options are less reliable because they rely on indirect evidence or information obtained from management, which may not be accurate or complete. References: CISA Review Manual (Digital Version), Standards, Guidelines, Tools and Techniques

Outsourcing the development of an e-banking solution when in-house technical expertise is not available can significantly reduce start-up costs. This is because the organization can avoid the expenses associated with hiring and training a full-time development team, purchasing necessary hardware and software, and maintaining the system1. While outsourcing can also potentially reduce the risk of system downtime, increase the ability to adapt the system, and provide direct oversight of risks, these benefits are not as immediate or guaranteed as the cost savings123.
References: Maxicus1, Forbes2, Strategy& - PwC3

The answer C is correct because preventive maintenance is outsourced to multiple vendors without requiring nondisclosure agreements (NDAs) would be of greatest concern to an IS auditor reviewing on-site preventive maintenance for an organization's business-critical server hardware. This is because outsourcing preventive maintenance to multiple vendors without NDAs exposes the organization to the risk of unauthorized access, disclosure, or modification of sensitive data and information stored on the servers. NDAs are legal contracts that bind the vendors to protect the confidentiality and security of the data and information they access or handle during the preventive maintenance. Without NDAs, the vendors may not have any obligation or incentive to safeguard the data and information, and they may misuse, leak, or compromise them for malicious or commercial purposes. This could result in financial losses, reputational damage, legal liabilities, or regulatory penalties for the organization.
The other options are not as concerning as option C. Preventive maintenance costs exceed the business allocated budget (option A) is a financial issue that may affect the profitability or efficiency of the organization, but it does not directly impact the security or availability of the server hardware. Preventive maintenance has not been approved by the information system (option B) is a procedural issue that may indicate a lack of coordination or communication between the IT department and the business units, but it does not necessarily affect the quality or effectiveness of the preventive maintenance. The preventive maintenance schedule is based on mean time between failures (MTBF) parameters (option D) is a technical issue that may influence the frequency or timing of the preventive maintenance, but it does not imply any risk or deficiency in the preventive maintenance itself.
References:
* What is a Maintenance Audit?
* How to audit your preventative maintenance schedule
* 5 Step Maintenance Management Program Audit
* How do you get effective Preventive Maintenance really?
* What is a Planned Preventative Maintenance Audit?