The report, Is Futurebuilders Working?, calls for an urgent change among public sector commissioners and charity providers in their approach to contracting.
"The unequal commissioning environment ... is a major threat to the success of the Futurebuilders model," the report says.
The commissioning problems mean organisations securing Futurebuilders loans cannot be sure of bringing in the cash to repay the debts, it adds. These payments enable the fund to recycle the cash and award loans.
One group that landed Futurebuilders cash says public sector commissioners "don't know how to buy and we don't know how to sell".