the donate button on your home page is not going to integrate with Fund Raiser Pro. If paypal posts an ipn or pdt from a transaction from that button it would be expected to log an error.
when the built in button in Fund Raiser posts to paypal it includes data that paypal will send back, a guid that corresponds to RowGuid in mp_PayPalLog
the PayPalPDTHandler.aspx and the ipn handler page lookup the row in the log to determine which provider handles processing, then invokes the handler provider to process it. if it can't find a matching provider it logs this error. this is how these urls are used for all ecommerce features and delegate the processing to the correct feature
so either the post did not correspond to a row in the paypal log and could not be processed, ie from some other unrelated paypal button like the one on your home page
or the provider is not plugged in. fund raiser includes its own files in the folders /Setup/ProviderConfig/paypalpdthandler and /Setup/ProviderConfig/paypalipnhandlers that plug in its handlers as providers. if the files were missing then it would also result in the same error, no matching provider found