Keep getting errors when doing event registration

Our version is 15.0.3.2042. We set up several events and open to public to register online. The registration process can successfully pass, but every time an error is generated in error log. We can see the error in 'error log' section in iMIS desktop system. Here is the error info, anyone knows what's wrong here?

HttpPath http://www.bccca.org/imis_public_org/Core/Events/Summary.aspx

HttpReferrer http://www.bccca.org/imis_public_org/Core/Events/Guests.aspx

HttpHost www.bccca.org

HttpAll HTTP_CONNECTION:keep-alive HTTP_KEEP_ALIVE:300 HTTP_ACCEPT:text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 HTTP_ACCEPT_CHARSET:ISO-8859-1,utf-8;q=0.7,*;q=0.7 HTTP_ACCEPT_ENCODING:gzip,deflate HTTP_ACCEPT_LANGUAGE:en-us,en;q=0.5 HTTP_COOKIE:ASPSESSIONIDSSQSCSDD=OJIJJOPBONGOHHBAMDJFDNND; ASP.NET_SessionId=fbs0n445xxvmro45jqfpcvjp; MeetingType=SOC; Asi.Web.Browser.CookiesEnabled=true; Login=0C134E8C31ACA7AF4B9D47F4938818C66713C6E866F9FCF0B33214F3C1D40AE694445C3D807EBF423454731A3DB775EE89D8A8DFD0A8E5A72996512EB82AB61CB9FACC469C5B09986CFCECF5B6257FCB0B0601CF9F125BCE6B2612D3D7E9E8D2458F3BAFECB0F5D052F328B9622DA24A; UserID=cgA1ycpnNos=; FirstName=Test; LastName=Test; FullName=Test Test; Company_ID=; Email=jason@graphicallyspeaking.ca; Organization=; SecurityGroup=0NboeGwWSd8=; ASPSESSIONIDQQQSCTCC=GEFHFKACIHFMEKJLIGKEHGCK HTTP_HOST:www.bccca.org HTTP_REFERER:http://www.bccca.org/imis_public_org/Core/Events/Guests.aspx HTTP_USER_AGENT:Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv:1.9.0.10) Gecko/2009042316 Firefox/3.0.10 (.NET CLR 3.5.30729)
Error Message The given key was not present in the dictionary.

Error displaying cart functions
Stack Trace at System.ThrowHelper.ThrowKeyNotFoundException() at System.Collections.Generic.Dictionary`2.get_Item(TKey key) at Asi.Bae.Web.Events.EventSummary.GetProductFunction(String functionCode) at Asi.Bae.Web.Events.EventSummary.DisplayFunctionInfo(CartEvent ce, Event ev)

at Asi.Bae.Web.Events.EventSummary.DisplayFunctionInfo(CartEvent ce, Event ev) at Asi.Bae.Web.Events.EventSummary.Page_Load(Object sender, EventArgs e)
Cookie Data ASPSESSIONIDSSQSCSDD=OJIJJOPBONGOHHBAMDJFDNND; ASP.NET_SessionId=fbs0n445xxvmro45jqfpcvjp; MeetingType=SOC; Asi.Web.Browser.CookiesEnabled=true; Login=0C134E8C31ACA7AF4B9D47F4938818C66713C6E866F9FCF0B33214F3C1D40AE694445C3D807EBF423454731A3DB775EE89D8A8DFD0A8E5A72996512EB82AB61CB9FACC469C5B09986CFCECF5B6257FCB0B0601CF9F125BCE6B2612D3D7E9E8D2458F3BAFECB0F5D052F328B9622DA24A; UserID=cgA1ycpnNos=; FirstName=Test; LastName=Test; FullName=Test Test; Company_ID=; Email=jason@graphicallyspeaking.ca; Organization=; SecurityGroup=0NboeGwWSd8=; ASPSESSIONIDQQQSCTCC=GEFHFKACIHFMEKJLIGKEHGCK

Error Type System.Collections.Generic.KeyNotFoundException

System.Exception
Error Date 6/1/2009 11:52:19 AM
User ID 1026