Hi @FredyDwi,
Please see the post here: Error 500 PHP Fatal error (there are others as well if you search for 'Cannot use ‘String’ as class name as it is reserved in …)
Before posting on the forum, please make efforts to search the forum for the errors you’re encountering and try suggestions that are offered in those posts (as per our guidelines: Forum Guidelines and Code of Conduct). If you have tried those suggestions offered in posts that resemble your issue, and you create a new post, please note that in your post.
Please note, as well, that the version of OJS that you’re using is no longer maintained or supported by PKP. I recommend that you upgrade to the newest version of OJS. However, other community members may wish to offer assistance with your question.
You may find the following resources helpful in preparing for and performing the upgrade:
These resources will introduce you to OJS 3 and how it is different from OJS 2:
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Setting up a Journal and Editorial Workflow video tutorials in PKP School
You may need to seek professional support to upgrade your installation. This can usually be acquired from the service provider that hosts or maintains your software, such as the technical support team at your institution or a third-party hosting provider.
If you are unable to get the support you need from your service provider, we recommend you consider exploring alternative providers.
-Roger
PKP Team