Your credit score is only one of many factors that go into a mortgage underwriters decision on whether or not to lend you money for purchasing a property. The score is used to give them a rough idea of how well you have serviced your previous and ongoing debts. A high score indicates that you are dependable in terms of making your repayments on time and for at least the minimum amounts expected by the creditor each week/month/year/whatever.
What a credit score does not tell them about a potential customer is how much debt they are currently carrying (their credit report will disclose this) and their ability to take on further liabilities.
It is possible to have a great credit score but already be teetering on the (theoretical) threshold of what you are able to repay each month based on your current income. Alternatively, you may have plenty of income and ability to repay debt, but have a terrible credit score because of poor debt management skills - making payments late or for the wrong amount.
There aren't really very many types of credit. If you already have an installment loan and credit cards then I doubt this would be used as a reason to decline a mortgage application. The most likely reason an underwriter would decline an application is if the applicants debt-to-income ratio is considered too risky for their portfolio. Different lenders are willing to take on different amounts of risk (while not a universal rule, the interest rates they charge typically reflect their risk tolerance - a lender with higher interest rates can take on riskier customers, using the extra revenue produced from higher interest rates to offset losses incurred when a higher proportion of of their portfolio defaults on payments).
All lenders will consider your total current debt, plus the amount you're asking to borrow, then compare that against your income (and to some extent your liquid assets). If you currently make $4,000 a month, have $600 in monthly loan and credit card repayments, and are asking for a mortgage that would require a $1200 monthly payment, then your debt-to-income ratio is (600 + 1200) / (4,000) = 45%. Some underwriters might be ok with this and approve the loan, others might want to see a lower percentage, say 43% or less.