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Users getting disconnected, java.lang.NoClassDefFoundError: Could not initialize class javax.imageio.ImageIO in logs

hi, i have had this chat server up for about 2 weeks. just today, i started noticing users were getting disconnecting/reconnecting etc. i see this in the log. can anyone point me in the right direction? I am running openfire 4.2.3 on centos 7

2018.11.01 08:44:04 WARN  [socket_c2s-thread-3]: org.jivesoftware.openfire.nio.ConnectionHandler - Closing connection due to exception in session: (0x000002BC: nio socket, server, /172.30.4.90:50376 => /172.30.0.14:5222)
java.lang.NoClassDefFoundError: Could not initialize class javax.imageio.ImageIO
        at org.jivesoftware.openfire.vcard.PhotoResizer.resizeAvatar(PhotoResizer.java:67)
        at org.jivesoftware.openfire.vcard.DefaultVCardProvider.loadVCard(DefaultVCardProvider.java:105)
        at org.jivesoftware.openfire.ldap.LdapVCardProvider.loadAvatarFromDatabase(LdapVCardProvider.java:307)
        at org.jivesoftware.openfire.ldap.LdapVCardProvider.loadVCard(LdapVCardProvider.java:237)
        at org.jivesoftware.openfire.vcard.VCardManager.getOrLoadVCard(VCardManager.java:239)
        at org.jivesoftware.openfire.vcard.VCardManager.getVCard(VCardManager.java:232)
        at org.jivesoftware.openfire.handler.IQvCardHandler.handleIQ(IQvCardHandler.java:115)
        at org.jivesoftware.openfire.handler.IQHandler.process(IQHandler.java:62)
        at org.jivesoftware.openfire.IQRouter.handle(IQRouter.java:369)
        at org.jivesoftware.openfire.IQRouter.route(IQRouter.java:112)
        at org.jivesoftware.openfire.spi.PacketRouterImpl.route(PacketRouterImpl.java:74)
        at org.jivesoftware.openfire.net.StanzaHandler.processIQ(StanzaHandler.java:348)
        at org.jivesoftware.openfire.net.ClientStanzaHandler.processIQ(ClientStanzaHandler.java:95)
        at org.jivesoftware.openfire.net.StanzaHandler.process(StanzaHandler.java:314)
        at org.jivesoftware.openfire.net.StanzaHandler.process(StanzaHandler.java:201)
        at org.jivesoftware.openfire.nio.ConnectionHandler.messageReceived(ConnectionHandler.java:177)
        at org.apache.mina.core.filterchain.DefaultIoFilterChain$TailFilter.messageReceived(DefaultIoFilterChain.java:690)
        at org.apache.mina.core.filterchain.DefaultIoFilterChain.callNextMessageReceived(DefaultIoFilterChain.java:417)
        at org.apache.mina.core.filterchain.DefaultIoFilterChain.access$1200(DefaultIoFilterChain.java:47)
        at org.apache.mina.core.filterchain.DefaultIoFilterChain$EntryImpl$1.messageReceived(DefaultIoFilterChain.java:765)
        at org.apache.mina.core.filterchain.IoFilterAdapter.messageReceived(IoFilterAdapter.java:109)
        at org.apache.mina.core.filterchain.DefaultIoFilterChain.callNextMessageReceived(DefaultIoFilterChain.java:417)
        at org.apache.mina.core.filterchain.DefaultIoFilterChain.access$1200(DefaultIoFilterChain.java:47)
        at org.apache.mina.core.filterchain.DefaultIoFilterChain$EntryImpl$1.messageReceived(DefaultIoFilterChain.java:765)
        at org.apache.mina.filter.codec.ProtocolCodecFilter$ProtocolDecoderOutputImpl.flush(ProtocolCodecFilter.java:407)
        at org.apache.mina.filter.codec.ProtocolCodecFilter.messageReceived(ProtocolCodecFilter.java:236)
        at org.apache.mina.core.filterchain.DefaultIoFilterChain.callNextMessageReceived(DefaultIoFilterChain.java:417)
        at org.apache.mina.core.filterchain.DefaultIoFilterChain.access$1200(DefaultIoFilterChain.java:47)
        at org.apache.mina.core.filterchain.DefaultIoFilterChain$EntryImpl$1.messageReceived(DefaultIoFilterChain.java:765)
        at org.apache.mina.core.filterchain.IoFilterEvent.fire(IoFilterEvent.java:74)
        at org.apache.mina.core.session.IoEvent.run(IoEvent.java:63)
        at org.apache.mina.filter.executor.OrderedThreadPoolExecutor$Worker.runTask(OrderedThreadPoolExecutor.java:769)
        at org.apache.mina.filter.executor.OrderedThreadPoolExecutor$Worker.runTasks(OrderedThreadPoolExecutor.java:761)
        at org.apache.mina.filter.executor.OrderedThreadPoolExecutor$Worker.run(OrderedThreadPoolExecutor.java:703)
        at java.lang.Thread.run(Thread.java:748)