[TYPO3-english] Class 't3lib_extMgm' not found

[Khondakar Readul Islam]

Dear everyone,

I am newbie, Today I installed typo3 in my local server. After then I was following the tutorial and installed Typo3 official template distribution. I thought I should try more so I tried to install extension package Image slider. After clicking the update button this message showed me 
'Class 't3lib_extMgm' not found'.

Not only that, when I was trying to refresh view every time shows the same below message

'Connection Problem

Sorry, but an error occurred while connecting to the server. Please check your network connection.'

However, I could understand that I need to learn more. Could anyone please help me to fix this problem and as well as where from should I start to learn this robust CMS  ?