vim NERD Commenter plugin gives errors while executing script

Question

I've installed the NERD Commenter on my vim 7.3 and when I try to use it's mappings, say, \cc (since I have \ as my leader key), it gives errors like these:

Error detected while processing function NERDComment..<SNR>7_CommentLines..<SNR>7_LeftMostIndx:
line   13:
E685: Internal error: get_tv_string_buf()
E116: Invalid arguments for function s:Left({'alt': 1}), s:Right({'alt': 1}), theLine))
E116: Invalid arguments for function s:IsCommented(s:Left({'alt': 1}), s:Right({'alt': 1}), theLine))
E15: Invalid expression: a:countCommentedLines || (!s:IsCommented(s:Left(), s:Right(), theLine) && !s:IsCommented(s:Left({'alt': 1}), s:Right({'alt': 1}), theLine))
E685: Internal error: get_tv_string_buf()
E116: Invalid arguments for function s:Left({'alt': 1}), s:Right({'alt': 1}), theLine))
E116: Invalid arguments for function s:IsCommented(s:Left({'alt': 1}), s:Right({'alt': 1}), theLine))
E15: Invalid expression: a:countCommentedLines || (!s:IsCommented(s:Left(), s:Right(), theLine) && !s:IsCommented(s:Left({'alt': 1}), s:Right({'alt': 1}), theLine))
Error detected while processing function NERDComment..<SNR>7_CommentLines..<SNR>7_RightMostIndx:
line   12:
E685: Internal error: get_tv_string_buf()
E116: Invalid arguments for function s:Left({'alt': 1}), s:Right({'alt': 1}), theLine))
E116: Invalid arguments for function s:IsCommented(s:Left({'alt': 1}), s:Right({'alt': 1}), theLine))
E15: Invalid expression: a:countCommentedLines || (!s:IsCommented(s:Left(), s:Right(), theLine) && !s:IsCommented(s:Left({'alt': 1}), s:Right({'alt': 1}), theLine))
E685: Internal error: get_tv_string_buf()
E116: Invalid arguments for function s:Left({'alt': 1}), s:Right({'alt': 1}), theLine))
E116: Invalid arguments for function s:IsCommented(s:Left({'alt': 1}), s:Right({'alt': 1}), theLine))
E15: Invalid expression: a:countCommentedLines || (!s:IsCommented(s:Left(), s:Right(), theLine) && !s:IsCommented(s:Left({'alt': 1}), s:Right({'alt': 1}), theLine))
Error detected while processing function NERDComment..<SNR>7_CommentLines..<SNR>7_CanCommentLine..<SNR>7_IsInSexyComment..<SNR>7_FindBoundingLinesOfSexyCom..<SNR>7_GetSexyComMarker..<SNR>7_HasCStyleComments:
line    1:
E685: Internal error: get_tv_string_buf()
E116: Invalid arguments for function s:Left({'alt': 1}) == '/*' && s:Right({'alt': 1}) == '*/')
E15: Invalid expression: (s:Left() == '/*' && s:Right() == '*/') || (s:Left({'alt': 1}) == '/*' && s:Right({'alt': 1}) == '*/')
Error detected while processing function NERDComment..<SNR>7_CommentLines..<SNR>7_CanCommentLine..<SNR>7_IsCommentedNormOrSexy..<SNR>7_IsInSexyComment..<SNR>7_FindBoundingLinesOfSexyCom..<SNR>7_GetSexyComMarker
..<SNR>7_HasCStyleComments:
line    1:
E685: Internal error: get_tv_string_buf()
E116: Invalid arguments for function s:Left({'alt': 1}) == '/*' && s:Right({'alt': 1}) == '*/')
E15: Invalid expression: (s:Left() == '/*' && s:Right() == '*/') || (s:Left({'alt': 1}) == '/*' && s:Right({'alt': 1}) == '*/')
Error detected while processing function NERDComment..<SNR>7_CommentLines..<SNR>7_CanCommentLine..<SNR>7_IsInSexyComment..<SNR>7_FindBoundingLinesOfSexyCom..<SNR>7_GetSexyComMarker..<SNR>7_HasCStyleComments:
line    1:
E685: Internal error: get_tv_string_buf()
E116: Invalid arguments for function s:Left({'alt': 1}) == '/*' && s:Right({'alt': 1}) == '*/')
E15: Invalid expression: (s:Left() == '/*' && s:Right() == '*/') || (s:Left({'alt': 1}) == '/*' && s:Right({'alt': 1}) == '*/')
Error detected while processing function NERDComment..<SNR>7_CommentLines..<SNR>7_CanCommentLine..<SNR>7_IsCommentedNormOrSexy..<SNR>7_IsInSexyComment..<SNR>7_FindBoundingLinesOfSexyCom..<SNR>7_GetSexyComMarker
..<SNR>7_HasCStyleComments:
line    1:
E685: Internal error: get_tv_string_buf()
E116: Invalid arguments for function s:Left({'alt': 1}) == '/*' && s:Right({'alt': 1}) == '*/')
E15: Invalid expression: (s:Left() == '/*' && s:Right() == '*/') || (s:Left({'alt': 1}) == '/*' && s:Right({'alt': 1}) == '*/')

But it actually successfully comments strings in my C file. But other mappings, like \cs, do not work at all with some other script errors.

Where to look to get rid of errors like these?