1. Read the error messages in Windows 98. Most of them should indicate the program or software that is causing the error message. One of the common issues of programs running on Windows 98 platform is compatibility. If the programs are not compatible, it will give you runtime errors. Identify these programs. Hit the Start button and select 'Settings.' Click on 'Control Panel' and double-click on 'Add or Remove Programs.' Scroll down the list to find these programs. Single-click on each of them and hit the 'Add/Remove' button. Click 'Yes' to confirm the uninstall.
2. Defragment your hard drive. Windows 98 tends to give out error messages when your files and folders are far from each other on your hard drive, thus making it difficult for 98 to access them. Navigate to the following location: 'Start' > 'Programs' > 'Accessories' > 'System Tools' > 'Disk Defragmenter.' Select the drive you wish to defragment. Typically it is your 'C:\' drive. Hit the 'Defragment' button and select 'OK.'

3. Update your operating system using Windows Update. A backdated Windows 98 may create issues and error messages from time to time. Hit the Start button and select 'Settings.' Click on 'Windows Update.' Follow the on-screen guided prompts to complete the update. Restart your computer.
4. Update the drivers on your Windows 98 if the error messages point to specific devices attached to your computer. Hit the Start button and select 'Settings.' Click on 'Control Panel' and select 'System.' Hit the 'Device' tab. Scroll down the list to see if you have hardware problems. If you do, there should an exclamation mark next to the device. Right-click on each of those devices and select 'Update Driver.'
5. Install an antivirus program. Error messages may occur due to virus infections. Avira, AVG and Kaspersky offer free downloads for Windows 98 users. See Resources to explore more free options for Windows 98 and make a selection to install the program. Restart the computer.