Please find below log when I try to preview the pptx.
Thanks.
2013-09-05 12:53:17,164 INFO [qtp354233797-14329:https://192.168.113.45:443/data/service/extension/com_zimbra_oo/rest/preview?target=PDF&auth=co&disp=i&view=html&fmt=native&id=257&ver=1] [] extensions - Checking conversion status for a :com.zimbra.cs.mailbox.Document
2013-09-05 12:53:17,165 INFO [qtp354233797-14329:https://192.168.113.45:443/data/service/extension/com_zimbra_oo/rest/preview?target=PDF&auth=co&disp=i&view=html&fmt=native&id=257&ver=1] [] extensions - Attempting to get a converter with key 'PDF:application/vnd.openxmlformats-officedocument.presentationml.presentation'
2013-09-05 12:53:17,165 INFO [qtp354233797-14329:https://192.168.113.45:443/data/service/extension/com_zimbra_oo/rest/preview?target=PDF&auth=co&disp=i&view=html&fmt=native&id=257&ver=1] [] extensions - Found an available converter:OOPdfConverter
2013-09-05 12:53:17,165 INFO [Uno:8103] [] extensions - Running beforeExecute
2013-09-05 12:53:29,417 INFO [Uno:8103] [] extensions - Before document export
2013-09-05 12:54:17,166 ERROR [UnoTimeoutTimer] [] extensions - Uno call has been timed out. Stopping the instance it was connected to for restart
2013-09-05 12:54:17,167 INFO [UnoTimeoutTimer] [] extensions - Disposing OO/Libre connection
2013-09-05 12:54:17,170 ERROR [Uno:8103] [] extensions - Error whilst disposing document
2013-09-05 12:54:17,170 ERROR [Uno:8103] [] extensions - Throwable caught while executing OO command:com.sun.star.lang.DisposedException
2013-09-05 12:54:17,170 ERROR [Uno:8103] [] extensions - Uno command was not successful on attempt:1
2013-09-05 12:54:17,170 INFO [Uno:8103] [] extensions - Running afterexecute
2013-09-05 12:54:17,171 INFO [Uno:8100] [] extensions - Running beforeExecute
2013-09-05 12:54:17,173 INFO [Uno:8103] [] extensions - Command timeout. Restarting Libre instance.
2013-09-05 12:54:17,173 INFO [Uno:8103] [] extensions - Attempting to stop OO/Libre on port:8103
2013-09-05 12:54:17,196 INFO [Uno:8103] [] extensions - Killing OO/Libre process:16682
2013-09-05 12:54:17,201 INFO [Uno:8100] [] extensions - Deleting lock file /opt/zimbra/mailboxd/work/.~lock.oo_uno_temp6358778500528717512.pptx#
2013-09-05 12:54:17,209 INFO [Uno:8103] [] extensions - Killing OO/Libre process:16697
2013-09-05 12:54:29,307 INFO [Uno:8100] [] extensions - Before document export
2013-09-05 12:55:17,171 ERROR [UnoTimeoutTimer] [] extensions - Uno call has been timed out. Stopping the instance it was connected to for restart
2013-09-05 12:55:17,172 INFO [UnoTimeoutTimer] [] extensions - Disposing OO/Libre connection
2013-09-05 12:55:17,173 ERROR [Uno:8100] [] extensions - Error whilst disposing document
2013-09-05 12:55:17,173 ERROR [Uno:8100] [] extensions - Throwable caught while executing OO command:com.sun.star.lang.DisposedException
2013-09-05 12:55:17,173 ERROR [Uno:8100] [] extensions - Uno command was not successful on attempt:2
2013-09-05 12:55:17,173 INFO [Uno:8100] [] extensions - Running afterexecute
2013-09-05 12:55:17,174 INFO [Uno:8101] [] extensions - Running beforeExecute
2013-09-05 12:55:17,174 INFO [Uno:8100] [] extensions - Command timeout. Restarting Libre instance.
2013-09-05 12:55:17,174 INFO [Uno:8100] [] extensions - Attempting to stop OO/Libre on port:8100
2013-09-05 12:55:17,195 INFO [Uno:8100] [] extensions - Killing OO/Libre process:16819
2013-09-05 12:55:17,198 INFO [Uno:8100] [] extensions - Killing OO/Libre process:16833
2013-09-05 12:55:17,212 INFO [Uno:8101] [] extensions - Deleting lock file /opt/zimbra/mailboxd/work/.~lock.oo_uno_temp6358778500528717512.pptx#
2013-09-05 12:55:28,645 INFO [Uno:8101] [] extensions - Before document export
2013-09-05 12:56:17,174 ERROR [UnoTimeoutTimer] [] extensions - Uno call has been timed out. Stopping the instance it was connected to for restart
2013-09-05 12:56:17,174 INFO [UnoTimeoutTimer] [] extensions - Disposing OO/Libre connection
2013-09-05 12:56:17,175 ERROR [Uno:8101] [] extensions - Error whilst disposing document
2013-09-05 12:56:17,176 ERROR [Uno:8101] [] extensions - Throwable caught while executing OO command:com.sun.star.lang.DisposedException
2013-09-05 12:56:17,176 ERROR [Uno:8101] [] extensions - Uno command was not successful on attempt:3
2013-09-05 12:56:17,176 INFO [Uno:8101] [] extensions - Running afterexecute
2013-09-05 12:56:17,176 INFO [Uno:8101] [] extensions - Command timeout. Restarting Libre instance.
2013-09-05 12:56:17,176 INFO [Uno:8101] [] extensions - Attempting to stop OO/Libre on port:8101
2013-09-05 12:56:17,176 INFO [Uno:8102] [] extensions - Running beforeExecute
2013-09-05 12:56:17,201 INFO [Uno:8101] [] extensions - Killing OO/Libre process:17173
2013-09-05 12:56:17,202 INFO [Uno:8101] [] extensions - Killing OO/Libre process:17187
2013-09-05 12:56:17,252 INFO [Uno:8102] [] extensions - Deleting lock file /opt/zimbra/mailboxd/work/.~lock.oo_uno_temp6358778500528717512.pptx#