As much as I like themes to personalize my Nokia Eseries device they are also a cause for the vast majority of all questions I can see in Eseries forums. Maybe we have the same difficulties installing such feature. But to cater those who do not know yet how to fix the problem, here is the answer.
Even if this have been covered extensively in the past I guess it is still an issue.

If you try to install a theme and see the above error message "Certificate Error. Contact the application supplier" You are trying to install an application that is not Symbian signed.
The solution is easy. Simply switch the setting in the Application Manager from "Signed only" to accept all - "Software Installation: All". You can find the application manager in the tools folder, then click on "Option" to bring up "Settings"
Another common issue is the "Expired Certificate" error. The certificate that the theme developer used may have expired. However, there is an even easier fix for this issue.

Simply set the date on your device back one year and then install the theme. After you successfully installed the theme don’t forget to set the time correctly on your device.
I do hope this helps you concerning E61i theme installation problem.
hii ,
good soltions but dude certificate exp solution is not working. the cell prompts that ‘’certificate expired or date stored is invalid'’
this cell has gone more smarter
Posted by akash at February 13, 2008, 8:44 pmthank you so much, you solved days of pondering
Posted by Joe at February 20, 2008, 5:53 amfor “’certificate expired or date stored is invalid’’ problem. you simply need to try different date. usually within 2 yrs from today(March 4 2008)
anyway, just try different date.
hey thanks for the solution. I was wondering what to do when i get this error.
Posted by pradeep at March 13, 2009, 6:00 pmthanks a lot.. this info was very useful
Posted by lindsay at July 9, 2009, 7:01 amhow do i delete themes that i cant even find in the application folder?? thanks
Posted by carol at July 10, 2009, 10:35 pmAll comments are moderated. Your comments will not appear here unless approved by the blog owner. Thank you.
The solution is great. I meet the same problem when I install the theme! I reset the phone.
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